I think people are misunderstanding the OP's issue. He has grade 5 unlocked, but he can't access higher than grade 1 remotely even when G1 is completed.
I had a similar issue with multiple HRP mods being capped at seemingly random levels for remote engineering (2,3,4 etc) and had to go to the engineer base to finish my upgrades. It was almost like there was a limit to the degree of remote engineering I could do and I was eating it up some unknown reserve quantity with each module upgrade. The first one capped out at 4, the second capped out at 3, and the last one capped out at 2. Was very strange. When I landed at the engineer, I verified that I had G5 unlocked, so that wasn't the issue. I was able to upgrade the same modules without issue at the engineer base. Not sure if it's a bug or an intended mechanic to limit remote engineering. If it's intended, then FD should spell it out in the patch notes or make a video explaining why. Otherwise it would just be frustrating and confusing to any player attempting remote engineering.
I suspect that it's a bug, kinda like the material limit being reset to 100 when you visit a mat trader.