You mean mimo function is not working on G34 after firmware update. could you please help us with few details that how did you confirm that the modem lost mimo function?

Before the firmware was updated by Xfinity., the old Wifi selection under web UI had the choice of MIMO option (under my remembering) but now has gone. No matter what, does the updated firmware support MIMO function ?

MIMO functionality is usually enabled by default and does not need any special settings to be configured through the modem's GUI web portal.

MIMO functionality remains unaffected by firmware updates.