I have another search issue.
In an earlier thread I spoke of occasionally not finding a result that was actually there, on a server search. I did not pursue as I could always find with Thunderbird on the PC, and it seemed rare anyway.
Today, on a good connection but not my own, I hit a different issue. Searching a folder with 22000 emails, it goes initially fairly fast, slows with each new batch searched (the message says "searching nnn/22000" and nnn increments in steps), it takes longer, and then longer, finally exiting with "network connection problem" or similar, after searching about 5 to 8% of the total.
My email server is on 1und1.de and is IMAP.