I tried several values in this process
pme_order = 8 / fourierspacing = 0.48
vs
pme_order =10 / fourierspacing = 1.20
try comparing to the the default:
pme_order = 4 / fourierspacing = 0.12
The pme grid dimensions need to be larger than pme_order (4) and in parallel larger than 2*pme_order for x and/or y