Hi,
Apologies for this – the usual cause for this is some form of conflict that Anvil can’t handle yet. The most straightforward workaround for now is for you to check the app out with Git via the command-line or a visual tool like Sourcetree or Fork, do the merge there, and push the result up to Anvil.
– Signed, The Person Who Has Most Of These Merge Issues On His To-Do List And Will Get To Them, He Promises!