Board Thread:The Flash discussions/@comment-4525203-20190508054640/@comment-3221148-20190514150150

Ninja72 wrote: A fairly popular theory is that this is LOT Thawne, who was not killed, but just trapped in the Speed Force. Although, I think this would be kind of stupid, it is still better than no explanation at all. The only explanation I see working is that when LOT Thawne was picking up versions of himself from across the time for the final battle, he actually picked up some version of Wellsobard (maybe when he was trying to travel in the time sphere) and sent him to Earth-X as a backup plan in case Black Flash DOES catch him and erase from timeline. After all, it's been established that timeline changes in one universe do not affect another universe. So running to another Earth, or sending one of his versions there, would certainly help Thawne.

Although that begs the question of how did he end up in the Iron Heights prison afterwards.