EDIT: (DEC 2021)
This is now confirmed to be a major graphical mirror error that effects all new AMD gpu (series 5000 and current 6000) in the way they handle mirrored surfaces (they reverse mirror objects).
In this case water reflections are reflecting what is on the opposite side of the ocean/game grid rather than above the waters surface (sky, ect)
This mirror graphic glitch also effects Sims 2 and Sims 3 with new AMD gpu's and requires a AMD driver fix for all sim games, please report this issue to AMD community! This glitch has existed for years still has not been fixed and will effect all new AMD gpu owners.
Comments
Are you using mods? If so, try the 50/50 method. It may reveal the culprit. Also, after each update, make sure that you update all mods. If you don't use mods, perhaps repairing your game might help? Also, try searching/posting here: https://answers.ea.com/t5/Bug-Reports/bd-p/The-Sims-4-Bugs. Someone there may be aware of the issue.
I wish you luck. Whatever is going on, it's very unsightly and I understand your frustration.
The big one on the island. Maybe it just effects that lot?
Both.
Sorry to hear that.
Have you searched the bug posts like @Cynna suggested? If there's no bug reports on it, you could post your own?
Hope it gets sorted for you.
Perhaps it’s an issue related to your graphics card?
I hope you get it sorted!
Anyway, mine does not look like that.
I'm patched to the most recent patch.
Here's a screenshot as close to your angle as I could get so you can see what mine looks like:
My advice is the usual, check your graphics card settings, check for driver and OS updates etc. Not sure what help I could give beyond that, but I hope you get it fixed soon!
Have you tried removing your CC and see if the problem persists? Bad CC can do unspeakable things. Also it could be some enlarged object placed on or off lot. I've seen people complain about some of the Cantina build pieces in Journey to Batuu that somehow became massively enlarged and displaced and blocked paths in Batuu. Check in a new save to see if the grid lines are still there.
I can only hope that with more people replacing/upgrading their graphics cards people will make more noise and fix the issue.
This not only effects the Sims 4, but reflected surfaces/mirrors in the Sims 2, Sims 3 and Sims 4.
This is not a problem with previous generations AMD graphics cards however.
To anybody considering upgrading their gpu, do NOT buy a current series AMD if you want reflections to work correctly in the Sims series games until AMD fixes this issue on a driver level.
https://answers.ea.com/t5/Bug-Reports/OPEN-Reflections-show-backwards-in-mirrors-Radeon-RX-6000-Series/td-p/10125588/page/7