I installed this mod late in the game when I wanted to upgrade my bricks to concrete, It did upgrade the bricks and concreted the whole construction area.
But then I wanted to upgrade the concrete to refined concrete so I enabled "Upgrade concrete tiles" and slowly concrete around one of the roboport was upgraded, but not the others.
I tried putting refined concrete under some of the roboports but nothing happened.
Only way I can get it to upgrade the concrete is to pick up the roboport and place it down again, it will then upgrade around that roboport but not the other ones.

I'm using Factorio 1.1.14 and Concreep 1.4.6

Roboports will periodically sleep if they haven't found anything to creep in a while. And the duration they sleep is proportional to the number of potential creeper roboports you have.

I've put a lot of optimizations into the creeping logic so it might be time to revisit how the sleep cycle works.

You can place a new roboport to force upgrading in that area.

I have 104 roboports and have picked up about 101 of them and placed them down again and it has upgraded the tiles around them.

I deliberate did not do that with 3 roboport just to see if the concrete was ever upgraded.
That was 6 days ago and about 20 hours of playtime has elapsed since then but the concrete is still not upgraded around those 3, so the sleep time looks to be huge.