Hi @planetpatrick ,
If it is a new build just verifying that the ram modules are installed in the DIMM A2 and DIMM B2 slots?
If one ram module only, it should be inserted into the DIMM A2 slot
This is from the [https://dlcdnets.asus.com/pub/ASUS/mb/LGA1151/TUF_Z390-PRO_GAMING/E14519_TUF_Z390-PRO_GAMING_UM_WEB.pdf|user manual]
[image|2238611]
(click on image to enlarge for better viewing)