This has always behaved like this, and I thought it should have been fixed by now. Upon restart, I have to disconnect the USB-C to the Plugable dock, then re-engage it for monitors to come into proper rotation and viewable (third monitor).
Unfortunately this is still an ongoing issue with Mac M1 users and though it it not common to see this issue with the UD-ULTC4K docking station it is an ongoing issue.
Here is more information on the issue itself and this information should be updated as soon as Apple issues an USB updater to address this.
For now we recommend that M1 Mac users experiencing this issue disconnect the docking station before computer boot up or wake and then only connect the docking after being logged in. This should assure the most consistent connection reliability.
If you have any questions, please feel free to let me know.