Here are some details:
Node-RED version: v1.0.2
Node.js version: v12.13.0
Linux 4.19.66-v7+ arm LE (on raspberry 3b+)
Dashboard version 2.19.0
The browsers used in our team are mainly chrome and firefox -at least I haven't seen anything else. I'm using firefox.
Unfortunately, I cannot tell if there are any messages in the console. I haven't checked it but will do so next time.
Deploy works just fine which is really strange. But it's definitely not just a ui/visual bug as it affects running the flow. E.g. the subflow pasted takes care of the role based authentication according to which we enable/disable ui widgets for the user. So when the input/output wires disappear in that subflow the app will go funky like certain things will be disabled or won't be shown for you which you shall be able to see, etc. At this stage we usually suspect that someone has changed the logic of a flow or something is screwed up in the db. The last thing we check if the wires are still in place.
Unfortunately, I don't know how to reproduce it. It happens once in a month or so (this was the third occasion) but I know that this info is of no help. Next time I'll check the console...