Thanks for doing the bisect.I was in the process of doing it myself and comparing disassembled byte-code when I saw the patch had been pushed. For anyone curious, this particular bug was a byte compilation error. When byte-compiled, org-capture-fill-template was attempting to compare strings via a jump-table-eq bytecode instruction instead of a jump-table-equal.
Resolved on Emacs master as of 949dd41c31dab69f7a5067bba324c28bb2cfbf8e