Firmware 2.1.2 "file block too large"

When I try to upgrade from 2.1.1-prodc with downloaded firmware Signed_OnlyKey_2_1_2_STD.txt I get “Error firmware file block too large”. I checked it against the hash and it’s fine. I see there was an old issue Firmware update fails · Issue #134 · trustcrypto/OnlyKey-App · GitHub which suggests I am using the wrong firmware however I have used the STD version for previous upgrades and I do not have the international key anyway. I am running App v5.3.6 is there anything else I can try?