After having upgraded to 5.20.3 I am no longer experiencing the bug. I leave to you the decision about chaning bugreport status.

$ xset q
Keyboard Control:
  auto repeat:  on    key click percent:  0    LED mask:  00000002
  XKB indicators:
    00: Caps Lock:   off    01: Num Lock:    on     02: Scroll Lock: off
    03: Compose:     off    04: Kana:        off    05: Sleep:       off
    06: Suspend:     off    07: Mute:        off    08: Misc:        off
    09: Mail:        off    10: Charging:    off    11: Shift Lock:  off
    12: Group 2:     off    13: Mouse Keys:  off
  auto repeat delay:  600    repeat rate:  25
  auto repeating keys:  00ffffffdffffbbf
                        fadfffefffedffff
                        9fffffffffffffff
                        fff7ffffffffffff
  bell percent:  50    bell pitch:  400    bell duration:  100
Pointer Control:
  acceleration:  2/1    threshold:  4
Screen Saver:
  prefer blanking:  yes    allow exposures:  yes
  timeout:  0    cycle:  600
Colors:
  default colormap:  0x20    BlackPixel:  0x0    WhitePixel:  0xffffff
Font Path:
  catalogue:/etc/X11/fontpath.d,built-ins
DPMS (Energy Star):
  Standby: 120    Suspend: 180    Off: 240
  DPMS is Enabled
  Monitor is On

$ qdbus org.kde.Solid.PowerManagement
/
/MainApplication
/local
/local/org_kde_powerdevil
/org
/org/freedesktop
/org/freedesktop/PowerManagement
/org/freedesktop/PowerManagement/Inhibit
/org/kde
/org/kde/Solid
/org/kde/Solid/PowerManagement
/org/kde/Solid/PowerManagement/Actions
/org/kde/Solid/PowerManagement/Actions/HandleButtonEvents
/org/kde/Solid/PowerManagement/Actions/SuspendSession
/org/kde/Solid/PowerManagement/Actions/WirelessPowerSaving
/org/kde/Solid/PowerManagement/PolicyAgent

$ ps aux | grep power
root        2258  0.0  0.0 462524  3760 ?        Ssl  nov08   0:00 /usr/libexec/upowerd
caterpi+  445463  0.0  0.0 614240  9440 ?        Sl   00:23   0:02 /usr/libexec/org_kde_powerdevil
caterpi+  506174  0.0  0.0 221588  2392 pts/1    S+   16:02   0:00 grep --color=auto power

Plasma 5.20.3
KDE Frameworks 5.75.0
Qt 5.15.1 (compilato con 5.15.1)
Il sistema di finestre xcb

It just happened again. I experienced it when screen was locked. By the way I could not experience it again in both unlocked or locked screen. I don't know why it is happening randomly

$ xset q
Keyboard Control:
  auto repeat:  on    key click percent:  0    LED mask:  00000002
  XKB indicators:
    00: Caps Lock:   off    01: Num Lock:    on     02: Scroll Lock: off
    03: Compose:     off    04: Kana:        off    05: Sleep:       off
    06: Suspend:     off    07: Mute:        off    08: Misc:        off
    09: Mail:        off    10: Charging:    off    11: Shift Lock:  off
    12: Group 2:     off    13: Mouse Keys:  off
  auto repeat delay:  600    repeat rate:  25
  auto repeating keys:  00ffffffdffffbbf
                        fadfffefffedffff
                        9fffffffffffffff
                        fff7ffffffffffff
  bell percent:  50    bell pitch:  400    bell duration:  100
Pointer Control:
  acceleration:  2/1    threshold:  4
Screen Saver:
  prefer blanking:  yes    allow exposures:  yes
  timeout:  0    cycle:  600
Colors:
  default colormap:  0x20    BlackPixel:  0x0    WhitePixel:  0xffffff
Font Path:
  catalogue:/etc/X11/fontpath.d,built-ins
DPMS (Energy Star):
  Standby: 120    Suspend: 180    Off: 240
  DPMS is Enabled
  Monitor is On
$ qdbus org.kde.Solid.PowerManagement
/
/MainApplication
/local
/local/org_kde_powerdevil
/org
/org/freedesktop
/org/freedesktop/PowerManagement
/org/freedesktop/PowerManagement/Inhibit
/org/kde
/org/kde/Solid
/org/kde/Solid/PowerManagement
/org/kde/Solid/PowerManagement/Actions
/org/kde/Solid/PowerManagement/Actions/HandleButtonEvents
/org/kde/Solid/PowerManagement/Actions/SuspendSession
/org/kde/Solid/PowerManagement/Actions/WirelessPowerSaving
/org/kde/Solid/PowerManagement/PolicyAgent
$ ps aux | grep power
root        2258  0.0  0.0 462524  3496 ?        Ssl  nov08   0:00 /usr/libexec/upowerd
user+  445463  0.0  0.0 614240  9896 ?        Sl   nov12   0:04 /usr/libexec/org_kde_powerdevil
user+  533763  0.0  0.0 221588   832 pts/3    S+   09:18   0:00 grep --color=auto power


Plasma 5.20.3
KDE Frameworks 5.75.0
Qt 5.15.1 (compilato con 5.15.1)
Il sistema di finestre xcb

Are you able to reproduce this issue in Plasma 5.25 or later?

Yes, I do confirm the bug on plasma-desktop-5.25.4

Cannot reproduce on 5.26.4

Unfortunately I started again to experience it on  5.26.4

Sounds like this should be debugged by looking for various power management inhibitors getting both good and bad samples, then comparing.
Some basic information can be obtained by running:
`systemd-inhibit --list`

Getting more specific information from KDE itself is tricky though:
- Apparently the Battery used to show power management inhibitors at least on laptops, but it currently doesn't according to Bug 474982 , so depending on the version you use, it may or may not help
- As described in Bug 426281 , desktop setups didn't get to enjoy the Battery applet's feature to begin with, but there's an extension linked there which could be helpful

I wonder if it's going to be related to media playback in the background even unknowingly. For example while I haven't tested if it messes with power management, Firefox has some odd problems with video playback, including videos not really stopping at the end but instead acting like the last chunk is being loaded forever, and I can see that still counting as video playback.

Is it still happening in any capacity in Plasma 6.2 or later?

🐛🧹 ⚠️ This bug has been in NEEDSINFO status with no change for at least 15 days. Please provide the requested information, then set the bug status to REPORTED. If there is no change for at least 30 days, it will be automatically closed as RESOLVED WORKSFORME.

For more information about our bug triaging procedures, please read https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging.

Thank you for helping us make KDE software even better for everyone!

🐛🧹 This bug has been in NEEDSINFO status with no change for at least 30 days. Closing as RESOLVED WORKSFORME.