The perform() method mixed pm.worked() with SubMonitor.convert() on the
same monitor, and called SubMonitor.convert(pm, 1) inside a loop. Both
patterns corrupt progress reporting: convert() resets the monitor's
remaining work, so repeated calls in a loop or after worked() discard
already-reported progress.

Replace pm.beginTask/worked/done and the in-loop SubMonitor.convert()
calls with a single SubMonitor.convert() up front, then split() for
each unit of work.