Statistically the odds of you getting 5 faulty 5900X is like getting struck by lightning twice.
How much troubleshooting have you done?
Sorry from five 5900x i have in last 1-2 year one is a dud, and one 7900x 1/1, the 5900x I shipped to seller, 7900x I still use as it work on +10 PBO (I plan to RMA it later when I do not need it as they are defo broken if do not work on stock), maybe its importer issue as we here buy CPU in kinda grey zone, ppl go to Hungary buy it and sell it to us for a fee
Also all 4 5900x works just fine with -20 PBO I have not tried more nor less
What speed is your RAM? The 5900X and all the other Ryzen 5000 series CPUs support up to DDR4-3200 officially and that's JEDEC standard DDR4-3200 (eq, CL22, 1.2v). Did you try disabling XMP (if you were running with XMP enabled)?
Nothing to do with ram I done dozen test with no XPM profile enabled, mostly have Kingston ram 3200 for DDR4 and 6000-6400 for DDR5
just RMA is complicated even if I detect issue in 24h of the time I received it, for last I am waiting for refund will see how it goes
Both cpu produced almost same WHEA error 7900x used in windows and new 5900x in linux where I monitor kernel log
Also the HU shop that sell it has defect rate 5900x is 0.8% and 5950x is 2.2% which to me is quite a lot