SUMMARY
This problem only occurs in System Monitor Plasmoid 2.8 (Debian 13.1).
Version 2.7 (Debian 12.12) works fine.

STEPS TO REPRODUCE
1.  Install the System Monitor Plasmoid (by Barry Strong)
2.  Hover the mouse on the different bars
3.  Observe different results as described below

OBSERVED RESULT
Proper behavior (2.7/Debian 12.12): When hovering the mouse over the bars I
have configured (CPU, RAM and Swap) a little window pops up with the
following: (for the RAM bar, the other bars have the correct displays for
CPU and Swap):

System Monitor - Memory

Total Memory:       15.52 GiB
Application Memory:  8.15 GiB
Buffer Memory:       0.10 GiB
Cache Memory:        6.85 GiB
Free Memory:         0.41 GiB

The problem (2.8/Debian 13.1): When hovering the mouse over the bars, no
matter which one, I only get:

System Monitor Plasmoid
Shows System Monitor Information

BUT! if I move the mouse very slowly at the very edge of the bars, I get a
very quick glimpse of the correct display as shown above, but it disappears
almost instantly.  It's like the mouse hover triggers the correct display only
at the very edge of the bars, possibly just 1 pixel.  Everywhere else I see
the generic message.

EXPECTED RESULT
That 2.8 would behave the same as 2.7

SOFTWARE/OS VERSIONS
The standard versions as distributed in Debian 12 and Debian 13.
$ kinfo
Operating System: Debian GNU/Linux 13
KDE Plasma Version: 6.3.6
KDE Frameworks Version: 6.13.0
Qt Version: 6.8.2
Kernel Version: 6.12.48+deb13-amd64 (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Core™ i7-4770S CPU @ 3.10GHz
Memory: 16 GiB of RAM (15.5 GiB usable)