Displacement sampling problem

[digil]

I have an often recurring problem with displacement and reflection. I attached a link with a video example (sorry I had to blackout main part as it's a work NDA project):

it's a small video sequence with a cigarette pack and HDRi rotating a bit (via UV offset animation) around the pack. The debossed lines on the edge of the pack are made via a 16-bit displacement map (high resolution one - about 8000 pixels in height for a total pack layout) with a Corona Displacement modifier applied. I've tried using different setting of Blur, Displacement size (Screen size from 2 pixels down to 0.1 pixels) and so on. It always gives some random result - sometimes it's fine and sometimes it gives this rhythmical "checker pattern" in the reflection. What's even more interesting - I managed to have VERY different results just by selecting the region (and selecting almost or exactly full screen size) and rerendering and getting perfect picture and then removing region and getting the pattern back.
Why is this happening and what can I do to avoid it?

https://drive.google.com/open?id=1-jqdxduezO1Ofg7n0nzHcebFNMWEw6Py

[PROH]

Hi. For any kind of animation with displacement, you should use World size instead of Screen size.

Hope it helps

[digil]

ooops

discovered I had an override in displace modifier, though I am DEFINITELY sure I checked it was off several times before. Weird!

[digil]

DOH!

The "Override" toggle parameter was ANIMATED! And there is a small bug that it doesn't show red border on keyframes. And I thought I was going crazy!  Uph...