TMP Assets keeps changing

My font asset keeps changing even though I don't edit the project. Sometimes simply just opening Unity is enough to trigger the change. I've battled with this for a while but have had no luck figuring out what is going on.

Here is part of the diff that Git keeps flagging:
View attachment 1039463

Sometimes it removes all that data and then if I commit that, later on it will try to add it all again.

Any ideas?