For me, it's explicitly that Senior stays on the right. Whether that be over or under another character, that remains to be seen. By the time I saw your message, I already have a save right before the problem. In this case, Senior is above other characters when he's stuck on the right. I just assumed that that's the issue people were talking about because it looks like he's a layer above the people and the dialogue. But it's possible that other people are experiencing a different problem. From all my years of doing tech support, I can firmly say that people suck at describing problems, let alone tech problems. Maybe asking them for screenshots of the problem would help too.
Since I already did the screen recording and have the save file right before the problem, I'm putting it here for reference and, if you need it, as a test case to make sure the fix does actually fix the problem. The video will show how I reproduced the problem and the result. The save is the same save I loaded in the video.