i know you said this 2 months ago, but i just encountered this question and don't know if you solved it yet. If you're on mobile a quick and easy fix to solve the "file size is too large" problem is to desktop the site, it will make mega think you are on a computer and will allow downloads of ANY size.
If you're already on computer however... then unfortunately i have no idea to help and guess to wait until Pomiart fixes the problem. Hope you see this and hope you're problem fixes/is already fixed!