Alas this is white label mem off eBay and fair bit of time has elapsed so not confident exchange would work. Minor miracle the ECC works at all given that
At some point I should try running it at slightly lower speed i guess. It’s very hard to troubleshoot something that only happens every month or two though
Never seen it fail a memtest but I can see it in the ECC stats since those cover weeks/months.
If you bought it from one of those ebay outfits that specialize in memory modules, they also often offer a lifetime warranty. Usually those sellers put their own sticker on the module. Worth a check.