I haven't seen any official posts or in-game news updates explaining the changes, but when I loaded up Harry Potter: Wizards Unite on my phone as I was preparing to take my morning walk today it asked me to update the app to the latest version. After I did I noticed that the first trace I captured gave me something like the "12th out of 5" fragments for the foundable I had captured. I went to the registry and it seems like a lot of things have been rebalanced.
Overview of the basic mechanic
For people who may not be familiar, Harry Potter: Wizards Unite is an "Augmented Reality" game like Pokemon Go, where the real-world GPS location of your phone is an element of gameplay. Also like Pokemon Go there's a "gotta catch 'em all" element to the gameplay -- the thing you're doing most often in the game is capturing "traces" of magical activity (by "tracing" spell patterns on your phone screen) which get recorded in your registry, which is like a magical scrapbook that functions like the pokedex in a pokemon game. One problem with this element of gameplay in Pokemon Go is that once you have completed your pokedex there's less of an incentive to play. An innovation to the mechanic in Wizards Unite is that the things you're collecting come in sets, so you'll want to capture a certain number of things in order to complete a "page" in the registry, which you can then "prestige" to level it up to reset the page and start collecting a new set. Basically it creates a mechanical reason to keep interacting with things even if you've already captured them once.
From what I can tell, there are two big changes. One is that the numbers of items required to complete sets seems to have been rebalanced, mostly making them easier to achieve. Since the number I had captured hadn't been reduced I had to spend a lot of time this morning prestiging pages that were now considered completed even though I still had a way to go on most of them yesterday. The second is that the number of fragments you've captured carry over when you prestige a level. Previously there wasn't as much point to capturing things that you had "maxed out" in your registry (you would still get XP for them, but not progress toward completing a registry page), now it seems like they count toward the "next" level in the page.
While having the floodgates opened this morning seemed a bit overwhelming to me, I think this is probably going to make things better going forward. Previously I found it kind of cool when different levels of completion on different pages would lead you to be more or less excited about different families of traces to interact with, since that created some dynamism in the game. But the extreme rarity of some fragments or "only available as rewards for high-level wizarding challenge" nature of some of the fragments made prestiging a page a pretty rare occurrence, so I found myself spending most of my time in the game being annoyed by encountering things that I didn't need. I think this change is likely to reduce that a bit. There's a possibility that it's too much of a good thing and maybe makes things so abundant that you never feel like you're hunting for anything, but I think it's too soon to say.
[edit 2020-05-09] Here is the official in-game update: