Should have updated this thread earlier. A new success:
27*2^7963247+1 is a factor of
F7963245 = 2^(2^7963245) + 1
Links to work unit (link will die soon) and Top 5000 entry. Links in my first post to Top 20, to fermatsearch.org and to prothsearch.com are unchanged. (Record F divisor currently belongs outside PrimeGrid.)
Finder's first F badge.
A list, generated on click, of all PrimeGrid's F divisors, with relevant links, is at https://www.primegrid.com/primes/primes.php?project=ALL&factors=F&only=ONLY.