OK I found what the problem was. It seems that UE 5.4 crashes if you use two or more nested Linked Anim Graphs in your animation blueprint.
For example, in my case, I use ALS V4 and Dynamic Flight. In ALS_AnimBP I have a Linked Anim Graph “CT_Flight_Example_Anim_Graph_ALS”, which itself contains “CT_Anim_Graph_Flight”, so it crashes during compilation of my player BP.
Remove “CT_Anim_Graph_Flight” and it works again. So the temporary solution is to only use one level of Linked Anim Graph. You can merge two Linked Anim Graph without too much difficulty, while waiting for a fix.
Before reporting the bug to Epic, we will need further feedback to be sure that the problem really comes from there.