The old issue #925 (Altar not building/disappearing while using TheOneProbe) seems to be still in Blood Magic. Back then not many informations were provided. I've invested some more time and this seems to happen either while holding a Probe or by setting showCanBeHarvested to 0 in theoneprobe.cfg/through ingame settings. While producing the error the logfile throws a NullPointerException in PlayerEvent$HarvestCheck. According to @McJty this problem is on Blood Magic's side and not on TOP's.

MC: 1.12.2
Forge: 14.23.5.2847
BloodMagic: 2.4.3-105
Guide-API: 2.1.8-63
TOP: 1.4.28

latest.log: https://pastebin.com/QX4XmxSL
Video: https://www.youtube.com/watch?v=0ZsUkeXKcVI

Issue on TOP: #54

If you need any other informations or testing, let me know.