Simple Server for ESP8266 firmware only works once, then needs 'redeploying'

Hi,

I am using a very simple Node-Red server to server a .bin file to an ESP8266 that requests it using the ESPhttpUpdate library.
"http in" node + "file edit in" node + "http out" node

[{"id":"7538e99c.ff6858","type":"http in","z":"773ae400.0de15c","name":"/LatestAGInterface/*","url":"/LatestAGInterface/*","method":"get","upload":false,"swaggerDoc":"","x":150,"y":20,"wires":[["f5203193.2d9508"]]},{"id":"f5203193.2d9508","type":"file in","z":"773ae400.0de15c","name":"Return latest FirmWare bin","filename":"/home/pi/AGFirmware/littlefs_0_1_2.bin","format":"","chunk":false,"sendError":false,"encoding":"none","x":460,"y":20,"wires":[["249aba2d.76d2d6"]]},{"id":"249aba2d.76d2d6","type":"http response","z":"773ae400.0de15c","name":"Send http reply","statusCode":"","headers":{"content-type":"text/html"},"x":720,"y":20,"wires":[]}]

It works fine and can deliver either a .bin sketch file or replace the contents of the littleFS, but it only works once.

If I restart the ESP it makes the request, which Node-Red gets, but the ESPhttpUpdate.update returns a

HTTP_UPDATE_FAILD Error (-11): HTTP error: read Timeout

If I leave the ESP in a loop making the request and just redeploy the flow (not making any changes to) it works fine, again only once ... any ideas of what is happening here?

Thanks for any suggestions

Pete