I've just lost my grave as well. Any way to retrieve it?

I still haven't found the grave even though I put a marker on it... strange that the marker remained but the grave (and all my best goodies) went with it ... sad times
I can't find any way of getting it back either. Tried reloading the steam save from when I logged out ... its still not there... Now I'm in the process of re making everything again. Fortunately I had saved some spare not so good armour so its tiding me over.

If you use the mod that resets dungeons this can happen as well, due to the mod. I just saw a 'new' dungeon reset mod go up on thunderstore a day or two ago that allegedly addresses this issue, by preventing the reset if a grave is present. The previous mod doesn't look to have that same grave-marker protection.
(Note, I don't use either mod, but that is what I gathered from reading their details).

Based on the mod description, if a dungeon resets when you have a grave marker 'inside' it takes your grave with it, so it makes sense that if a game update does the same reset the same thing would happen.

Yup - same here - hit a Dvergr by mistake and they turned on me. Went back, killed them and my grave had gone.

I have had low trust on graves for a while. I always mark the skull & crossbones with a map marker upon respawning, just in case. Map markers hold up well, I have never lost one.

Don't remember that sort of thing happening. Graves should persist until someone empties their inventory. But for the brief duration when they spawn, they seem to be affected by gravity (the way I remember it anyway), maybe it could have fallen through the dungeon or appear above ground?

I never lost a grave but I do recall surtling cores respawning in a crypt I had previously cleared after a patch.

None of the mobs respawned though.

Haven´t lost a grave so far.
Do you have cloud save enabled for valheim? I have heard that it can cause weird things to happen very similar to what you have described. I´d recommend disabling this function for valheim.