4 sourced reports, with what to check before you buy. Each one links to the page it was reported on.
Costly or dangerous
WF-1000XM5 left earbud failed within a month with static/buzzing/popping
A verified owner reports the left earbud failed within a month of purchase, with very low volume and static/buzzing/popping.
What to check. A buyer should test both earbuds immediately on arrival and keep proof of purchase, because one owner's unit failed within the first month with static/buzzing/popping and very low volume. This is a unit-level failure, so check the warranty/return window early.
Sony acknowledges white noise/static under Active Noise Canceling on WF-1000XM5
Sony's own documentation confirms that a continuous static/white noise is heard whenever the Noise Canceling function is on, and the only remedy it gives is to turn ANC off.
What to check. Expect a faint hiss/static whenever ANC is enabled; Sony documents this as inherent to the ANC implementation rather than a per-unit defect. If that hiss bothers you, the only remedy Sony offers is to disable ANC, which defeats the main selling point.
WF-1000XM5 charging case intermittent charging failure reported
The same long-term owner reports an intermittent charging problem that a service-centre claim did not resolve.
What to check. One owner reports intermittent charging problems where the service-centre claim came back unresolved and dirty. Verify the charging case actually tops up the earbuds before relying on it, since a failed case leaves the buds unusable.
WF-1000XM5 right earbud stopped working completely after ~2.5 years
A long-term owner reports the right earbud stopped working completely after about 2.5 years of use.
What to check. A long-term owner reports one earbud dying completely after ~2.5 years, which is past the typical warranty period, so the replacement cost falls on the buyer. Treat the earbuds as a consumable with a limited lifespan rather than a permanent purchase.
These reports come from the pages linked under each item: owner forums, repair guides and workshops. They are not a diagnosis of any one unit, and a careful check of the one you are buying still applies.
Text from the Kriko Premium earbuds catalog, version 0.1.1, under the CC-BY-SA-4.0 license.