aof6 1.10.1
deepmoblearning-refabricated-0.5.12-BETA+1.19.2
You're in Grave Danger 1.4.9

I've built a trial area high up in the sky around y 120-50 ish
while going through a skeleton trial(the highest difficulty one) I died and spawned somewhere quite far.
I used /home tp (base) command to get near to a waystone
and then used the waystone to get to another waystone which is few blocks away from the trial area
(I bridged out a few blocks from the area)
After I arrived at my grave I found out that I couldn't pick up my grave, I tried lots of weird combinations of things.
Then I tried to break trial keystone with my hands and it didn't break, as if I was trying to break a protected block.
The same was for blocks around it, such as the trial area ground blocks, I even used pickaxes.

Did the trial fail normally (you should see a chat message if so) or did all mobs just despawn? It's likely the trial was on some weird state. Either way, I'm thinking of adding a tag of blocks that can be broken during trials regardless of state, so any graves can be retrieved without much hassle

Seems similar to #91, I'll take a look into it.

I've added the trial grief whitelist tag, hopefully other modders will add their graves to it eventually.
As for the trial issue - I'll keep tracking it on #91. Thanks for reporting!