Hello,
I’ve discover this curious bug right known. When I use a shaman card who transform my monster in another monster with or less one level (or more too), yogg with this 15 stars doesn’t have friend.
So the game change yogg into same another yogg, with this power of titans used (like a photo) but I can reuse a power I have already make.
I think the problem is for all titans but yogg is probably the simple to create this bug.
Or maybe it normal because it’s yogg 
Actually Yogg is the only one where you’ll have that issue
Titans can’t be generated by random effects, evole/devolve included. But Yogg is the only 15 mana minion, with no 14 or 16 to transform into. Some other cards like Conjurer’s Calling even destroy him without summoning anything.
You will never have another titan staying in place after such an effect being applied to them, they will transform as normal.
I have invoked yogg, not generated it.
But I confirm the regeneration broke the effects and the game is lost, so in the doubt, all are reset but not the light
Yes you played Yogg yourself, but you said you tried to transform it with an evolution/revolution/devolution effect, which are effects that “generate” minions. But there’s no eligible minion to transform into in the 14/15/16 mana pools, not even Yogg itself is in the 15 mana pool