I just played a very highroll fortune game. Managed to get the 250 cashout and got the fortune emblems. Went level 10 and bought every 5 cost i could find.
I was soon at 8Irelias, 8Wukongs and 6Hweis. This was early in Stage 5. I Also held every other 5cost, but saw that I couldnt hit those because someone else with a decent amount of hp held atleast 1. No Irelia, no Wukong and no Hwei was played or held by anyone else. I also saw them rolling so these units couldnt have been perma locked in a shop. I rolled the 9 Fortune gold on level 10 through the entirety of stage 5 and for the love of god couldnt hit any of them 3 star. At the end my shops contained no 5 costs anymore. All were out of the pool. Still no Irelia and no Wukong or even a 7th Hwei. Kept scouting and looking where the units are. No one had them and again, they were rolling so its not even possible to lock the unit in shop. If you have seen 9 Fortune you know how much gold I rolled on level 10 and I only hit Wukong because Hwei printed it at the end.

When I saw the boards in the end I looked what boards the other people had. 5th place had 1 Irelia and 1 Wukong and 4th place played a Hwei 2. For the last 3 or 4 rounds only me and 2 other people were still alive. The people holding my 5 costs were out of the game and yet they werent showing up in my shops. The units werent put back into the pool when the players died. My shops werent containing any 5costs when no one else was holding them. I dont know if this bug is exclusive to 9 Fortune or 5 costs or something else but unless I am missing something I cant explain this any other way than it being bugged.