According to what I have read in the code UpdateUpdater should fallback to CheckoutUpdater in case of issues, which it does.
But in the first analysis it seems the code checking the state of the working copy locks the WC database in case of the new working copy format (.svn/wc.db)
A workaround is to use the CheckoutUpdater (verified)
The issue looks as follows (for full stack see attachment):
This can be replicated with this short Jenkinsfile script