I have the same waterblock and a 360 rad cooling the CPU, northbridge, VRM's and a RTX2080 with no problems. The fact that your temperature shoots right up would suggest that the cpu isn't transmitting the heat to your block. If it were then your outgoing fluid should be warm to the touch if its running that hot.
A few things I can think of are:
1) You forgot to remove the clear plastic cover from the new waterblocks copper surface. (don't laugh I've done it)
2) Not enough thermal paste or the block isn't tightened down enough
3) Wrong restrictor plate installed on waterblock (even then tho I wouldn't think it would get that hot)
4) The CPU needs to be lapped, you could check how flat the top of it is with a straight edge.
Is it a new cpu or a new waterblock?
Is the waterblock itself getting hot? (and the fluid inside it)
Can you see the fluid moving?
Is the reservoir warm to the touch?
Make sure the CPU is making good contact with the waterblock. Sounds like that may be where your problem is.