Please submit a bug-report as described in this document:
It’s important that you report these issues together with a reproduction project if you want them to get fixed. If you don’t do it, it might be a long time until someone else reports them or until Unity Technologies find them.
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I’ve seen this affecting other asset store assets too.
On my own stuff, I had to set “fixedHeight” to 0 when creating a style based that was using TextArea as base.