Hi there!
I've been dealing with an ongoing issues regarding some of my animated graphics with transparent backgrounds made in After Effects gaining a colours pixelated outline (examples in attached images). It's seems selective on what it effects and when it effects it. Soemtimes it's just made a jagged pixel-shaped edge instead on being the smooth shape I made.
It doesn't occur when I initially import. Always after I've closed the programme and restarted, but then even if trying to replace it by re-importing or even render it fresh from After Effects it stays pixelated.
It happened with my old PC and it's doing it with my newer one too. Just in case it's hardware related I'll drop some details but like aforementioned. It happened on my older PC that was far less capable than this one. Please let me know if any more details are required to help figure this out.
CPU: 12thGen Intel i7-127000
RAM: 32GB
GPU: Inten UHD Graphics 770 & NVIDIA GeForce RTX 3070