Shadow priest talents defaulting to different build when adding new hero talents

When I add new hero talents while leveling, it keeps changing to my ST build and I lose shadow crash. Then when I choose to swap back to the M+ build after selecting the new talents and it says I’ll lose my build. I have to reselect the hero talents again and relearn shadow crash. I know for sure that I have not directly swapped the build and I had not recently swapped specs. I was using shadow crash while in the delve a few minutes prior to the issue.