A quick note about the sizing of the reram cell. I suppose the minimum size of the memristor layer can only be 300nm. If you go below this size, for some strange reason, the reram layer does not contain the via layer and only uses the r1c layer and metal 2 layer. So just a heads up and precaution that while doing a layout dont go below 300nm.

I think you have an old version of open_pdks. That problem was fixed four months ago:

posted: April 19, 2022 at 2:00am     version: 1.0     revision: 310
...
Corrected the GDS output and input for the ReRAM layer which was, in a nutshell, all screwed up.