One suggestion .. since you are the one creating that array
why dont you add from the begining the information needed (msg.sequences) that the modbus-flex-sequencer will later need.
Also its better to remove the second delay you have in your flow.. i dont think its needed since Modbus Config has its own queue of modbus commands.
Added a modbus-queue-info node to monitor how many commands are queued.
Example Flow (untested) :
[{"id":"a8b7f1f2.cd6ca","type":"modbus-flex-connector","z":"5847b7aa62131d37","name":"","maxReconnectsPerMinute":4,"emptyQueue":false,"showStatusActivities":true,"showErrors":false,"server":"3f55d524.d93c72","x":630,"y":1460,"wires":[["38cbf3bc.9ad9d4","ea1493b6.7819b"]]},{"id":"38cbf3bc.9ad9d4","type":"debug","z":"5847b7aa62131d37","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":770,"y":1400,"wires":[]},{"id":"ea1493b6.7819b","type":"modbus-flex-sequencer","z":"5847b7aa62131d37","name":"sequencer 1","sequences":[{"name":"1","unitid":"1","fc":"FC4","address":"10009","quantity":"1"}],"server":"3f55d524.d93c72","showStatusActivities":true,"showErrors":true,"logIOActivities":false,"useIOFile":false,"ioFile":"","useIOForPayload":false,"emptyMsgOnFail":false,"keepMsgProperties":false,"x":910,"y":1460,"wires":[["60595176.16f1d8"],[]]},{"id":"60595176.16f1d8","type":"debug","z":"5847b7aa62131d37","name":"output","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":1090,"y":1460,"wires":[]},{"id":"e2d77eca.b789e","type":"inject","z":"5847b7aa62131d37","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payloadType":"date","x":115,"y":1460,"wires":[["7a7de6e0.750358"]],"l":false},{"id":"7a7de6e0.750358","type":"function","z":"5847b7aa62131d37","name":"f1","func":"var devices = [\n {\n \"delta\": 1, \"nazwa\": \"ED_9373\", \"connectorType\": \"TCP\", \"tcpHost\": \"10.0.0.202\", \"unitId\": 8, \"sequences\": [\n { \"name\": \"Foo\", \"unitid\": 8, \"fc\": 4, \"address\": 10009, \"quantity\": 1 },\n { \"name\": \"Bar\", \"unitid\": 8, \"fc\": 4, \"address\": 10010, \"quantity\": 1 }\n ]\n },\n {\n \"delta\": 2, \"nazwa\": \"ED_9376\", \"connectorType\": \"TCP\", \"tcpHost\": \"10.0.0.132\", \"unitId\": 2, \"sequences\": [\n { \"name\": \"Foo\", \"unitid\": 8, \"fc\": 4, \"address\": 10009, \"quantity\": 1 },\n { \"name\": \"Bar\", \"unitid\": 8, \"fc\": 4, \"address\": 10010, \"quantity\": 1 }\n ]\n },\n {\n \"delta\": 3, \"nazwa\": \"ED_9377\", \"connectorType\": \"TCP\", \"tcpHost\": \"10.0.0.201\", \"unitId\": 4, \"sequences\": [\n { \"name\": \"Foo\", \"unitid\": 8, \"fc\": 4, \"address\": 10009, \"quantity\": 1 },\n { \"name\": \"Bar\", \"unitid\": 8, \"fc\": 4, \"address\": 10010, \"quantity\": 1 }\n ]\n },\n {\n \"delta\": 4, \"nazwa\": \"ED_9375\", \"connectorType\": \"TCP\", \"tcpHost\": \"10.0.0.203\", \"unitId\": 9, \"sequences\": [\n { \"name\": \"Foo\", \"unitid\": 8, \"fc\": 4, \"address\": 10009, \"quantity\": 1 },\n { \"name\": \"Bar\", \"unitid\": 8, \"fc\": 4, \"address\": 10010, \"quantity\": 1 }\n ]\n },\n {\n \"delta\": 5, \"nazwa\": \"ED_9379\", \"connectorType\": \"TCP\", \"tcpHost\": \"10.0.0.204\", \"unitId\": 5, \"sequences\": [\n { \"name\": \"Foo\", \"unitid\": 8, \"fc\": 4, \"address\": 10009, \"quantity\": 1 },\n { \"name\": \"Bar\", \"unitid\": 8, \"fc\": 4, \"address\": 10010, \"quantity\": 1 }\n ]\n },\n {\n \"delta\": 6, \"nazwa\": \"ED_9374\", \"connectorType\": \"TCP\", \"tcpHost\": \"10.0.0.203\", \"unitId\": 3, \"sequences\": [\n { \"name\": \"Foo\", \"unitid\": 8, \"fc\": 4, \"address\": 10009, \"quantity\": 1 },\n { \"name\": \"Bar\", \"unitid\": 8, \"fc\": 4, \"address\": 10010, \"quantity\": 1 }\n ]\n },\n {\n \"delta\": 8, \"nazwa\": \"ED_9380\", \"connectorType\": \"TCP\", \"tcpHost\": \"10.0.0.202\", \"unitId\": 7, \"sequences\": [\n { \"name\": \"Foo\", \"unitid\": 8, \"fc\": 4, \"address\": 10009, \"quantity\": 1 },\n { \"name\": \"Bar\", \"unitid\": 8, \"fc\": 4, \"address\": 10010, \"quantity\": 1 }\n ]\n },\n {\n \"delta\": 9, \"nazwa\": \"ED_9381\", \"connectorType\": \"TCP\", \"tcpHost\": \"10.0.0.203\", \"unitId\": 6, \"sequences\": [\n { \"name\": \"Foo\", \"unitid\": 8, \"fc\": 4, \"address\": 10009, \"quantity\": 1 },\n { \"name\": \"Bar\", \"unitid\": 8, \"fc\": 4, \"address\": 10010, \"quantity\": 1 }\n ]\n },\n {\n \"delta\": 7, \"nazwa\": \"ED_9378\", \"connectorType\": \"TCP\", \"tcpHost\": \"10.0.0.131\", \"unitId\": 10, \"sequences\": [\n { \"name\": \"Foo\", \"unitid\": 8, \"fc\": 4, \"address\": 10009, \"quantity\": 1 },\n { \"name\": \"Bar\", \"unitid\": 8, \"fc\": 4, \"address\": 10010, \"quantity\": 1 }\n ]\n }];\n\n\n\n//msg.payload = { 'connectorType': 'TCP', 'tcpHost': '127.0.0.1', 'tcpPort': '10502', 'unitId': 2 } return msg\n\n\ndevices.forEach(dev => {\n\n node.send({\n \"topic\": dev.nazwa,\n \"payload\": {\n \"connectorType\" : dev.connectorType,\n \"tcpHost\": dev.tcpHost,\n \"tcpPort\": \"502\",\n \"unitId\": dev.unitId\n },\n \"sequences\": dev.sequences\n });\n\n})\n\n\n\nreturn null;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":210,"y":1460,"wires":[["32ebc461.d791fc","9a8b464d.122a98"]]},{"id":"32ebc461.d791fc","type":"debug","z":"5847b7aa62131d37","name":"","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":310,"y":1400,"wires":[]},{"id":"9a8b464d.122a98","type":"delay","z":"5847b7aa62131d37","name":"","pauseType":"rate","timeout":"5","timeoutUnits":"seconds","rate":"1","nbRateUnits":"10","rateUnits":"second","randomFirst":"1","randomLast":"5","randomUnits":"seconds","drop":false,"outputs":1,"x":400,"y":1460,"wires":[["a8b7f1f2.cd6ca"]]},{"id":"bf8eea292ceaa8d3","type":"modbus-queue-info","z":"5847b7aa62131d37","name":"","topic":"","unitid":1,"queueReadIntervalTime":1000,"lowLowLevel":25,"lowLevel":75,"highLevel":150,"highHighLevel":300,"server":"3f55d524.d93c72","errorOnHighLevel":false,"showStatusActivities":true,"updateOnAllQueueChanges":false,"updateOnAllUnitQueues":false,"x":1000,"y":1560,"wires":[[]]},{"id":"3f55d524.d93c72","type":"modbus-client","name":"","clienttype":"tcp","bufferCommands":true,"stateLogEnabled":false,"queueLogEnabled":false,"tcpHost":"10.0.0.203","tcpPort":"502","tcpType":"DEFAULT","serialPort":"/dev/ttyUSB","serialType":"RTU-BUFFERD","serialBaudrate":"9600","serialDatabits":"8","serialStopbits":"1","serialParity":"none","serialConnectionDelay":"100","serialAsciiResponseStartDelimiter":"","unit_id":"0","commandDelay":"100","clientTimeout":"1000","reconnectOnTimeout":false,"reconnectTimeout":"2000","parallelUnitIdsAllowed":false}]
[EDIT]
Correction .. the second delay between Connector and Sequencer is needed after all, because the Modbus Flex Connector takes its time to actually change the modbus config settings.
For sure you cannot have both set at 10sec because by the time sequencer does its read a new message will arrive at connector messing up the settings .. and all hell will brake lose.
You have to play with the timing of the 1st and 2nd delay. the 2nd has to be less