I am NO expert but been on the trad journey for 3 years now and picked up a ton from folks here and dont want to leave you hanging here on your 1st post.
First off not what you are asking but learning or relearning good form at 55# is going to make your job a lot tougher and maybe get some 40 or 45# limbs.
Second, some could be form and from a form issue am curious if you are drawing to 28
Third if your are able to learn on 55# and using ok form the 400 spine maybe stiff with the point weight you are using possibly even at 55#s if you are not drawing 28 and the weight is in the low 50s would make it even worse. The arrow being too stiff will hit left bare shaft. Do you have any 100 grain inserts or heavier tips 180 to 220 range to try to see if you can weaken it up for a test?
Lastly welcome and enjoy the process!