holgerkaengu,
I just wondered if you had tried:-
1, making sure that you do not have a download limit set under 'Download Controls' in Pegasus's POP3· settings?.
2, increasing the 'time-out' values in Pegasus's POP· and SMTP settings?.
I can understand the frustration when it worked prior to the Avast update, but I am taking a big guess that it is to do with time-outs because prior to the update mail would be routed through the localhost (127.0.0.1) and this would pass through very quickly and/or possibly form a buffer that masked any time-out settings.
Good luck.