Your last image you attached is kinda surprising. It does not show the problem you discuss since the maximum latency it shows is 43ms....Looking at it again it does show spikes in the first hop the average is pretty low.
What is strange is you are seeing a lot of jitter to the first hop which is your router. If you had not said this was powerline I would have assumed it was ethernet. In the first hop on ethenet you generally see all packets at the minimum latency. Yours you see your AVERAGE is 26ms higher than the minimum. This jitter amount is consistent to the end of the trace so it has to be the first connection causing this.
I would test with a actual ethenet cable run over the floor if there is no other option. You need to determine if it is the powerline units causing this or something else. A long ethernet cable to test with is going to save you time chasing the wrong thing.
It is not real common for powerline units to cause issues, especially if you have the newer AV2 based ones. Unfortunately there are still houses that powerline has problems in.