TCL TV cannot update RokuOS

I have a TCL TV model 65Q825 that has been failing to update RokuOS for a few weeks now.

When I query the TV for updated software, it reports that it is using software version 15.0.4.5519 and is ready to update to a new version. I allow the update to proceed. The TV reboots, and it reports that it is still using software version 15.0.4.5519. 

This has been happening for a long enough period of time that I have seen three different RokuOS versions offered to me.

My Roku wireless speakers and subwoofer have been updating OK. Not sure if that is relevant.

No error code is ever displayed to me. I performed a factory reset on this TV and the problem persists. TCL and Roku technical support pointed the finger at each other.

Any ideas I can try?