Yes, don't use the Celestron driver with a Synscan HC. While the command sets are similar and some commands will work not all commands will. The Celestron driver uses a number of low level commands that are passed by the HC directly to the motor controller. The Synscan HC was designed to emulate some of these but I very much doubt that it supports all of them.
There is I believe a separate Synscan driver.
Logs that show the communication between the driver and the HC would help. These are available but need enabling.
I'm the current maintainer of the Celestron driver.

BTW the Ra Offset messages you mentioned are there to help to remove a systematic error in the Celestron HC slew implementation.

Finally, as a general principle I would avoid doing a sync on an equatorial mount close to the pole. Tiny differences in position in Ra can have a huge effect on the pointing.
Chris

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