Apple's new version of macOS, High Sierra 10.13.4, renders monitors and displays connected through third-party screen extender software unusable.
Monitors connected through DisplayLink technology go blank after a user upgrades to the latest macOS version. The Duet Display and Air Display screen extenders experience the same issue.
DisplayLink - whose technology allows multiple displays to be connected to a computer through USB, ethernet, and wi-fi - recently confirmed the issue following a flood of complaints from Apple users who had downloaded the macOS update.
It said the problem affected the current DisplayLink driver - version 4.1 - and advised users to either downgrade to macOS 10.13.3, or download a new DisplayLink driver (4.3) that partially addresses the issue.
"[Version 4.3] ... will enable clone mode, but not mirror or extended mode displays in 10.13.4. If you require mirror or extended mode displays, we recommend that you stay on macOS 10.13.3 or earlier at this time," the company said.
In a forum post a DisplayLink product manager said the issue had "the highest business priority" in the company.
"We understand that this loss of functionality on OS upgrade is potentially disruptive for our users and customers," he wrote.
"We thank you for your patience and will provide an update on this situation, as soon as we have further information to share."
The developer of Duet Display - a Mac app that turns an iPad or iPhone into an extra display for a Mac - similarly advised its users to refrain from installing the latest version of macOS; the app stops functioning after the update.
Avatron Software, owner of the Air Display screen extender, offered its users the same warning.
"Air Display users: Please don’t update your host Mac to macOS 10.13.4," it said.
"It introduces severe WindowServer bugs that crash most inelegantly when you connect to a virtual monitor like Air Display (or its competitors). 10.13.3 still works fine. Hopefully Apple will fix 10.13.4 soon."
Apple has been contacted for comment.