Constant periodic stutter with no identifiable cause after S30 update.

PC stats: 5700x3d, 9070XT, 24gb ram @ 3000mhz, Windows 10, SSDs, all thermals fine etc. It's a well working system and has been for years. 

Ever since the S30 update I stutter every 2 seconds, sometimes every one second. Prior to this the game ran fine. It's highly periodic and repeatable. Below is a plot of my frametimes with an inset showing a portion of the data which clearly shows the highly periodic nature of the stutter. 

I have checked all the obvious potential causes of this that could be my fault but nothing solved the issue: 

• No RBG software, overlays or anything like that is active. 
• I have wiped GPU drivers from offline safe mode with DDU and reinstalled. 
• I changed the realtek ethernet controller with the windows default one (I use wired connection)
• I have disabled windows game mode, AMD game modes from BIOS and anything of that nature in Adrenlin. 
• I've ran it without Adrenlin, driver only install.
• Disable Logitech mouse software entirely.
• Slightly outdated GPU drivers and BIOS run the same as current versions. 
• I have thoroughly inspected the system while Apex is running with Windows Performance Monitor and Analyzer and can't find any processes to blame. Except maybe something due to anticheat, which isn't surprising, but I can't get to the bottom of this one.
• LatencyMon says everything is all good when playing Apex. 
• The GPU and CPU are not cycling in and out of sleep or low power states. 
• Halo Infinite, another EAC game, works fine. 
• Armored Core and RoR2 work fine at max settings. 
• I don't have any cheat software, reWASD or anything like that installed.
• Easyanticheat.exe or whatever it's called it seemingly not spiking resource use according to task manager but the plots are too low res in there to tell. 
• Easyanticheat.exe or whatever  it's called doesn't spike on this timescale in WPA analysis and neither do any of the other processes that seem to obviously belong to it.  But processes that are less clearly labeled that might belong to EAC do spike, albeit with low CPU usage. 
• I even had a lengthy chat with Claude and tried all its suggestions, which was basically all the stuff I already did, and it agrees it's probably not my system. 

So as far as I can tell, this isn't my fault. It might be EAC related, according to my WPA data, but I'm a bit out of my depth trying to crawl through the stack and thread data.  The processes that clearly belong to EAC don't spike like this, but I think there are threads or processes that run under Apex or just system that are EAC related. Their names make them not obvious and it's a deep rabbit hole of expanding the stack to see what's in there.  But given the symptoms it seems like there has to be something EAC is checking on my system constantly and causing this issue.