Premiere Pro transitions make image darker

What is going on with Adobe stock transitions in Premiere Pro? I started noticing it in Film impact transitions and thought it happened because they were third-party. Now I used Premiere Pro transitions like Page turn and it is clearly the problem in Premiere Pro itself. Here is a side-by-side comparison screenshot showing that while the transition is happening the image looks darker than it is (look at the blurred letters in the background - is is a nested image + blurred image (gaussian blur used)). As soon as the transition ends the image becomes what it is. I tried both whith GPU acceleration and without it - all the same. PP is 25/5/0 and it happened on erlier versions as well, so I doubt my problem is solved in the current version available.