we are struggling with a project that has things (arduinos as clients) communicating to our MQTT broker (mosquitto) running on a DigitalOcean droplet (inside a docker). We have about 200 things at different locations sending about 20msg per minute each. Last week - after months without any issues - 20 clients suddenly were not able to connect to the server/publish anymore although they have been online. Today 4 other clients “went offline” the same second.

The latter 4 clients were fixed by simply restarting them. With the aforementioned 20 clients, we were able to test one (remotely) and we reflashed it (nothing changed with MQTT settings though) and it was then able to connect to the broker again...

First we thought it was a network issue but it all seems to be fine. Can you help us troubleshooting the issue? We run a DigitalOcean droplet for our mqtt server.

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    There’s not nearly enough information here to properly debug, but it sounds like a counter overflow to me. Things work fine for months, then an integer overflows, your code wasn’t prepared to deal with reading garbage, boom, dead in the water. Just a hunch. – RubberDuck Apr 24 '19 at 10:23
  • Please post the code, versions of libraries and IDE used. – MatsK Apr 24 '19 at 10:42

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