duplicate key violates unique constraint pg_toast_635216540

Hi,

For the last 6 months or so we've had an intermittent issue while doing a
data import with a simple update statement.  The fix that we've found for
this issue is to REINDEX TABLE <tablename>;


Has anyone seen this error before?

Again, the error is: duplicate key violates unique constraint pg_toast_<>

Thanks,

Paul