Hi Kanchana, I fully understand that I can't edit the join layer. Yes, the difference b/w my use case and yours is that I am making edits to other feature layers in the same web map that the join layers are in and my need to sync is what is causing the sync errors. I have confirmed this by doing what you said. I created a dummy feature service and a new join which I enabled sync on. I then added both to a new web map to confirm the behavior. In the Android version of Collector, the error provides which layer is not syncing and it is the join layer. It appears that Collector still tries to run the synchronizeReplica operation on the join layer even though it is not editable and there are obviously no edits.
I tried to disable editing on the join layer to force Collector not to run the synchronizeReplica operation, but this doesn't appear to work either. It looks like the web map disables editing by adding a capabilities property to the layer in the operationalLayers object.
"capabilities": "Query,Extract,Sync,ChangeTracking"
When I add a capabilities property to the join layers in the operationalLayers object, I either can't download the map or it still errors when syncing. I've tried it without 'ChangeTracking' as well since ChangeTracking would not be a valid capability for the join layer, but it didn't work either.
As I mentioned in my response to Khaled, I think my best course of action is just to live with the errors for now. Thanks again for your help.