User random lockups

We have one user of our Vaadin application who experiences UI lockups at random but fairly frequent intervals. We haven’t been able to reproduce the issue or identify the root cause. (Vaadin 23.3.15)

In the most recent incident, this was captured in the Javascript log. Does this provide any pointers as to where the problem might lie?

FlowClient.50f41ee4.js:1 Uncaught (in promise) Error: Client is resynchronizing
at FlowClient.50f41ee4.js:1:44108
at Array.forEach ()
at N2 (FlowClient.50f41ee4.js:1:44083)
at Ky (FlowClient.50f41ee4.js:1:35336)
at z.eb (FlowClient.50f41ee4.js:3:78698)
at x (FlowClient.50f41ee4.js:1:32725)
at Map.forEach ()
at G2 (FlowClient.50f41ee4.js:1:47725)
at wp (FlowClient.50f41ee4.js:3:51262)
at uo (FlowClient.50f41ee4.js:3:38088)
at z.rb (FlowClient.50f41ee4.js:3:76654)
at z.O (FlowClient.50f41ee4.js:3:89050)
at XMLHttpRequest. (FlowClient.50f41ee4.js:1:26420)
at kd (FlowClient.50f41ee4.js:1:17546)
at A3 (FlowClient.50f41ee4.js:3:5709)
at XMLHttpRequest. (FlowClient.50f41ee4.js:1:28181)

If you’re using a proxy, could be that there’s a proxy timeout; If you’re using Push with websockets, make sure the configured websocket and proxy connection timeout is at least as long as the websocket timeout in the app server.

See here a longer answer about this topic: Unexpected message id from the client (sync ids different) · Issue #12640 · vaadin/flow · GitHub

We have already checked the proxy timeout configuration, but we will check that again. The odd thing is that other users at this site do not have the same difficulty.

This is a corporate client and I know there are a lot of proxy and security layers involved. I just wish we had a better understanding of the cause so we could provide guidance to them as to what to tune.