You should test each kit separately and if any errors found then RMA the full kit.
When you have a RAM mismatch it is because of Latency. RAM kits are binned at the manufacturers factory in order to ensure the DIMMs are compatible.
I ran the memtest and I got one error in test 6 which was like a one bit error or 2 bit error I went into logs and it said my memory latency was like 20 ns
2020-12-01 21:26:09 - cpu_cache_speed - Memory latency: 21.338 ns
2020-12-01 21:35:46 - [MEM ERROR - Data] Test: 6, CPU: 3, Address: 7CB587700, Expected: 00008080, Actual: 00008000
2020-12-01 21:35:50 - MtSupportRunAllTests - Test execution time: 63.903 (Test 6 cumulative error count: 1)
^ that was the error message
I don't feel like waiting 2 weeks to rma my new ram but I feel like its the right thing to do? will 1 error be fine? this is my other acccount