Universal Control, Onscreen keyboard on iPad broken when connected to smart connector/stand for charging

Universal Control and onscreen keyboard of iPad Pro 13 (M4, iPadOS 26.x) from MacBook Pro (M2 Pro, 26.1) is broken when using an iPad stand with a built-in smart connector for charging. I use the Kuxiu articulating wall-mount stand, and have a desktop version at the office. This configuration previously worked on iPadOS 18.

If I put the iPad on the stand, and it is charging, it only appears in Universal Control on my Mac as a device to which I can extend or mirror the screen. And that works as expected. But it does not appear as an iPad that I can control with my mouse and cursor. It might show up in the list, but it does not work.

Further, if I want to type directly on the iPad Pro, the onscreen keyboard does not activate when I go to any text field (Spotlight, web browsers, etc). It is not because it's connected to my nearby MBP, because the Mac does not show the iPad as connected, and the Mac's mouse and keyboard have no effect on the iPad.

I have rebooted both devices. I have disabled and re-enabled Handoff (iPad) and Universal Control (Mac) multiple times without effect. The keyboard only returns if I remove the iPad from the stand. Same with Universal Control. The current workaround is just to slip a piece of paper between the pins on the stand and the contacts on the iPad. Then all works (because it's the same as being off the stand), but obviously no charging.

As indicated intially, this all worked just fine before the 26 system upgrades.