I have had the same issues and thought I was being blackballed. lol I noticed a GIANNI task with 28 hours that I should have been in 18th for a while, then down to 24, then off the page. Then I started looking for my other tasks and could not find my name on any of them until I got to this one https://www.gpugrid.net/workunit.php?wuid=11694725. I should have been on several of those listings going by my personal stats at the top right on the page, but only the one could be found in the lists. Some of these tasks are hours, days, and over a week old, but not as many as only one in one type have been duplicate top 30 times.

I'm ranked second on the ADRIA_FAAH_WT_ (super-long workunit) list with this task (done in 19.86 hours),
while in the "Your personal records" table I see this task (done in 17.65 hours),
which is faster than the present 1st ranked result (done in 17.86 hours).