SUMMARY
Text-only sensor widgets are empty after booting into KDE Plasma 6.5 beta (and beta 2). Toggling between another display mode and text-only brings it back again until a relog. Other appearance variants do not seem to trigger this behavior on relog, for instance the network usage one (graph with text) or the color grid.

This issue does not occur on Qt 6.9, meaning this is a regression in the 6.10 release candidate.

STEPS TO REPRODUCE

1. Install Arch Linux or an Arch-based distribution (e.g. CachyOS) with KDE Plasma (Wayland)
2. Add an entry into /etc/pacman.conf to enable the kde-unstable repository in order to get Plasma 6.5 and the Qt 6.10 RC: https://wiki.archlinux.org/title/Official_repositories#kde-unstable
3. Perform a system update with pacman -Syu
4. Reboot the system
5. Set up a text-only sensor widget with some sensor entries (like GPU VRAM or RAM usage)
6. Log out
7. Log back in

OBSERVED RESULT
The contents of the widget are gone while the title remains

EXPECTED RESULT
The contents of the widget remain visible

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 6.4.90
KDE Frameworks Version: 6.18.0
Qt Version: 6.10.0
Kernel Version: 6.16.7-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 20 × AMD Ryzen AI 9 365 w/ Radeon 880M
Memory: 32 GiB of RAM (27.2 GiB usable)
Graphics Processor: AMD Radeon 880M Graphics

Downstream KDE bug report: https://bugs.kde.org/show_bug.cgi?id=509671, it turned out that it was a Qt regression there