Hello Nick,
This problem surfaced a few days ago when Google updated its Chrome browser for Windows. (It occurs in version 96.) The problem does not occur on Firefox or on the Mac.
Apparently there are quite a few problems caused by this Chrome update so we expect that Google will fix them soon.
A workaround is to make a new document from the Getting Started document that already has the Mammals data in it. In fact, here is a link to a shared document you can use for this purpose.
I hope Google fixes there problem soon!
Bill