Note: This bug seems to have been fixed in the latest snapshot 21w18a. Its probably related to the fact that a bug about extreme lag when generating terrain was fixed in this snapshot. I'm extremely happy this has been fixed because I always play with the preview data pack and its so bad I've been playing on 1.16.5 instead of snapshots. I can finally get back on my 1.17 worlds without experiencing extreme lag whenever I move!

now here's what the bug was about:

When I try to record, stream or just have OBS Studio open(which is a recording/streaming software) in this snapshot, the game lags, but not exactly lag. The screen occasionally freezes for a short time and when you die and respawn, it stays frozen for a long time. This problem has slowly gotten more frequent for me to the point where it freezes every 1 to 15 seconds and I rage quit my live stream. I have tested and it does not do this in 1.16 and I have not experienced it at all until I played in the latest snapshot (21w16a) This bug makes it very annoying to record/stream and I even tried reinstalling OBS Studio. (I did not reinstall minecraft because A, It only effects this version and B, I don't know how long it takes to reinstall minecraft or even how. ) It also seems to do this more when I move faster. 

I don't know what other programs cause this or if its actually related to RAM or Memory usage, but I'll put everything for environment in a screenshot attachment of F3 mode, because that's the only place I can find that actually gives me most of my PC specs. (in the screenshot the terrain generation is not a bug, its from attaching the caves and cliffs data pack to a world right after generating it[very interesting] )

Note: after some testing, It sometimes may not do it at all at first when a world is new, and the longer you play on the world the worse it gets. Other times, the lag starts as soon as you make your world. You also don't have to have something like OBS Studio open but I think it makes it occur more when it is open.  I don't know as much about it as I thought I did, but whatever is causing it, it is pretty annoying for the screen to freeze up often, and only happen specifically in this snapshot.  Also all times I have experienced this were in a world with the most recent(as of reporting this bug) caves and cliffs preview data pack, two in single player and one on a locally hosted server. I have only been able to recreate this bug once in other worlds since I first reported this bug, because it usually does not start until I have spent some time on the world. This one other world was a caves generation world using the most recent caves and cliffs preview data pack. In every caves generation world generated using this data pack, this bug has occurred for me. Also in worlds where this bug occurs, it can take forever to load the world, sometimes even crashing my game while joining the world. 

To see the lag this creates it is shown on my recent live streams on my YouTube channel, here is a link to one of them. https://youtu.be/j4qgcNKZ7W8?t=608 watch on low volume or muted if you care for your ears(I like to say stuff near the mic and it gets loud) just a quick warning 

Steps to Reproduce:
1.  Open minecraft version 21w16a or 21w17a and play minecraft. 

2. Travel at high speeds in different worlds using the caves and cliffs preview data pack. It will lag a lot
3. Repeat in other versions and it should not do this. 

hopefully you guys can reproduce this and fix it but if you cant reproduce this I guess I'll have to try reinstalling minecraft, thanks in advance