FSX Import Showcase

I’ve imported some FSX AI planes and after watching them for a few takeoffs I noticed that they lose altitude whilst banking, sometimes dropping from over 1500ft to as low as 600ft above the ground before recovering. At first I was thinking this was a result of the import process but I’ve noticed the default generic models have this same issue. I’d like to fix it but I don’t know where to look in order to correct the issue. Anyone point me in the right direction?