I actually noticed something similar when booking a few weeks ago. I had done a lot of searches so I was clearly interested, but results for the same (slightly niche) search on a "clean" device (VPN + cookie-less browser) returned the same:

Basically, a certain price was the "starting from" price but that was irrelevant as I was looking for more expensive direct flights. They were initially advertised at €x. Then after a few permutations of searching, I go to book the flight. You can literally even see the price update from €x to €(x+50) when you are on the page. I thought it was strange so I did a Google Flights search and found it for €x. But once again, when I clicked my way through to the AY website, the price literally updated in front of my eyes to €(x+50). I almost considered booking via OTA but then decided I didn't want to deal with trying to get OTA flights as "Value" (the x+50 flight was Pro but the other way was Value) given that I am getting the trip reimbursed anyway. In retrospect I wonder what the mechanism updating the price was and could I for example have tried disabling jscript on the page?