It looks like that it was caused by some internal changes on the server side, and this prevents databricks-connect from working. You can always disable this check by setting environment variable DEBUG_IGNORE_VERSION_MISMATCH to value 1 (export DEBUG_IGNORE_VERSION_MISMATCH=1 in the console before executing databricks-connect test) – you can also set this environment variable in the PyCharm.
Update: it should be fixed by Databricks Connect 6.4.2 that was just released.
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