I do have the very same issue with Ryzen 2200G on an MSI B350M. HDMI works during boot up (BIOS) but as soon as Win10 with installed AMD graphics driver (18.5.1) starts HDMI does no longer work, I need to use DVI then (with 1920x1080 only since this is the max for DVI with 2200G).
Without installed AMD driver, i.e. with standard Windows graphics driver HMDI works under Windows!
See also my post in MSI forum: No HDMI output under Win10 (64) with MSI B350M PRO-VDH and Ryzen 3 2200G