One of the commonest causes of ‘strange behaviour’ that our users have reported seems to be Jalview running out of memory. Memory errors can cause some operations to fail silently - with no warning, annotations may disappear from the alignment window, and web service calculations (apparently) never finish.

You should be able to see something in the error log - see the instructions for bug reporting on how to view this. If you do see ‘Out of memory’ or ‘Cannot allocate stack’ or ‘HeapAllocationError’ type messages, then you might be able to fix it by increasing the memory available to jalview.