Conflict with "Better mobGriefing GameRule" mod. With certain mod settings, the survival inventory disappears. To avoid this, set the "inherit" rule for the "Creeper" mob in the "Better mobGriefing GameRule" mod, and set the "TNT Utils" mod for the destructibility of blocks by the creeper.
Conflict with TNT Utils mod. With certain mod settings, the survival inventory disappears. To avoid this, set the "inherit" rule for the "Creeper" mob in the "Better mobGriefing GameRule" mod, and set the "TNT Utils" mod for the destructibility of blocks by the creeper.
MC 1.12.2
The most recent versions of both mods.

Sorry for not answering for so long, I want to pick TNTUtils up again after pretty much only working on other projects.

I followed the reproduction steps that you wrote in Judge40/BetterMobGriefingGameRule#31 with only TNTUtils and BetterMobGriefingGameRule (tried it both with 6.1.0 and 7.1.0), but I couldn't reproduce it either. Maybe it is an interaction with a different mod. As pointed out by Judge40, can you give me the list of mods, configs and logs for when this happened?