Updated, February 3: An LG spokesperson confirmed with Ars that the 5K UltraFine monitor isn't adequately shielded from EM radiation, and that displays manufactured after February 2017 "will be fitted with enhanced shielding."

Furthermore, existing displays can be retrofitted with extra shielding—if you own the 5K UltraFine, and you're having issues, you should "contact your nearest customer service centre for prompt service."

Curiously, the spokesperson said that the Wi-Fi router interference problem only occurs when the router is behind the display within a distance of 0.6m (2ft).

LG didn't comment on the other issues that customers are reportedly experiencing. Apple still hasn't responded to our request for comment.

Original story (January 31)

The spiritual successor to Apple's Thunderbolt Display, the LG UltraFine 5K monitor, which only started shipping out from the Apple online store this week, appears to suffer from a major fault: when placed within two metres (6.5ft) of a wireless router, the display starts to flicker; move it really close, and the monitor goes black and becomes unusable. An LG Electronics support person confirmed the issue, saying it "only happens for the 5K monitors we have, not other LG monitors."

If that wasn't bad enough, 9to5Mac's Zac Hall reports that his LG 5K monitor, under the duress of a nearby Wi-Fi router, can freeze the MacBook Pro that it's plugged into, forcing a reboot to bring it back. When he moved the router (an Apple AirPort Extreme) from beside the monitor to another room, everything went back to normal.

A support rep for LG Electronics confirmed that the 5K monitor can be adversely affected by a nearby wireless router and said that the issue doesn't affect any other LG monitors. Hall was asked to place the router "at least 2 metres away" from the monitor and "to let us know" if the problem still persists after that.

If you take a look at the monitor's product page on the Apple website, customer reviews started pouring in from January 25; a few of them are positive, but a lot of them are negative. Some of them explicitly call out the router-proximity issue, but many other major issues are also described: kernel panics on the host machine, random flickering even when there are apparently no nearby sources of wireless radiation, and USB devices not being reliably detected when plugged into the monitor.

As for why the LG UltraFine 5K (currently discounted to £884 due to Apple's ongoing USB-C discount) is so dramatically affected by a nearby wireless router, we can make a few educated guesses. Clearly, some key part of the monitor hasn't been correctly shielded from electromagnetic radiation, and that part of the monitor is probably oscillating at a harmonic of Wi-Fi (2.4GHz or 5GHz) radiation. Best-case (but unlikely), the point of weakness is a faulty Thunderbolt 3/USB-C cable. The more likely victim is the clock generator on the LCD panel controller or USB controller.

Hopefully the EM interference flaw is easily fixable with a bit of additional shielding so that future batches of the LG 5K monitor don't suffer from flickering, blackouts, and locked-up host machines. Judging by how many negative reviews the monitor has accrued in just a few days, and the myriad other reported issues, perhaps there's a major quality control problem, or the design of the monitor is inherently flawed.

With Apple retiring the Thunderbolt Display and "working closely" with LG to create the 5K UltraFine monitor, you have to assume that Apple will be keen to quickly fix things up.

We've asked both Apple and LG for comment and will update this story if they respond.