Caused by rBfffba2b6530. In above commit, the buttons rnaindex [-1 for entire arrays like colors] was not used anymore for the entire function body of `ED_autokeyframe_property` (previously in `ui_but_anim_autokey`). Replacing the index with 0 (in the array case) is indeed necessary for `BKE_fcurve_find_by_rna_context_ui`, prior to rBfffba2b6530 this was taken care of by using `ui_but_get_fcurve` instead [which did this internally]. But using an index of 0 (instead of -1) for the entire function body of `ED_autokeyframe_property` fails for the array part later, namely `insert_keyframe` needs -1 here. Now just replace the index for //finding the FCurve//, but use the original for //inserting the keyframe//. Could be backported to 2.83 LTS. Reviewers: campbellbarton, sybren Subscribers: