Fix too tight assertions in annotation saving

[fm3]

Fixing regression introduced in #7290

Steps to test:

• Save skeleton with just a few clicks, should work
• Save skeleton with imported large nml, should work
• Save skeleton with a few clicks PLUS an import of a large nml, should work (this was the error case before)

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• Updated changelog

[normanrz]

So the problem was that all transactions with just 1 group would fail?

[fm3]

So the problem was that all transactions with just 1 group would fail?

Only in requests with single-group transactions and bigger transactions