Found the issue, that the twinned eidolon's base form: biped was not correctly applied. As a result the companion was missing ability scores, saves and an increased move speed. I was already using LegacyKing's version of the lotfw_abilities_companion.lst PU Support file, which is also the one I edited to "fix" the issue. In line 7 of the LST-File i added BONUS:VAR|Pool_UnchainedEidolonForm|1 to give the eidolon acces to the abilitypool so you could chose biped manually istead of trying to add it automatic. This solved most of the issues beside the increased move speed which I added extra using BONUS:MOVEADD|TYPE.Walk|10 .