Problem merging revisions in online compiler

Hello,
I am trying to merge two committed revisions in the online compiler and I am repeatedly encountering an “unhandled error occurred” popup.
image
I have tried switching the working version to each of the revisions I am trying to merge together, but the error arises in both cases. The revision tree currently looks like this, I am trying to merge revisions 56 and 57.
revision tree

Are there any possible fixes I could try to successfully merge these revisions?

Best regards,
Catherine