You have 1 Foo Lion summoned and have rejuvenated 1 to above the starting AP and/or MP, and the other Foo Lion dead.
If you Summon the Foo Lions, the existing one is reset to starting AP/MP/HP and loses any excess AP/MP. It seems like a bug. To me, I think one of the following should happen to the existing Foo Lion:
1. Left alone when the missing one is summoned
2. Rejuvenated when the missing one is summoned
3. Forcibly dismissed and a brand new one summoned as you can only summon a pair at once