The database tasks are sort of like the old left-hand / right-hand thing.
The previous clash didn't end properly, and is stuck in processing. However, the part of that process that puts back the "search for opponent" tab, did end properly (sort of).
So, while the left hand is trying to search for a new opponent...the right hand is bogged down in processing trying to end the previous clash. And won't let the left hand do its job, because according to the right hand the club is still in an active clash that hasn't ended yet.
I'm no IT guy...but I'm guessing that if you got those previous clashes to end properly...things should sort themselves out. In theory...