Review your error log.
From how you describe it I would expect one animation is for another skeleton or invalid, thrown an error and causing the t pose.
The obvious: are you sure the animations don’t end in a t pose? If so, just cut the frames.
The nasty: you can use a pose snapshot but you have to trigger it on/off accurately in BP.
You may want to review some of the topics in here with much more complex situations and explanations about combos.