Hi Paulos.
Sounds like you’ve run out of ram to me. After Effects will ram preview as much of the work area as it can. When it runs out it loops back to the beginning and plays out as much as its been able to cache.
The green line issue you have there is the cached ram dropping itself out and being replaced by the new part of the comp that you are previewing on the fly.
I’d recommend droping the ram preview resolution down if you haven’t already and maybe try changing your layer quality settings to draft, or setting your 3d settings to draft 3d if its a comp with lights.
Hope this helps,
Cheers,
Ben