SUMMARY
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MTP access to device doesn't work after device connection. I need to close dolphin and re-open it.
https://forum.kde.org/viewtopic.php?f=225&t=168662&p=444513#p444513 seems to be uneffective.
***


STEPS TO REPRODUCE
1. Open Dolphin
2. Connect MTP-enabled device

OBSERVED RESULT
Disk & Devices offerto to open and mount: clicking on mount&open doesn't do anything.
Dolphin shows the device on the side bar. Clicking on it gives an error that the device isn't available.
Closing and reopening Dolphin make it work until next logout.

EXPECTED RESULT
Disk & Devices offerto to open and mount: clicking on mount&open opens dolphin on the device content.
Dolphin shows the device on the side bar. Clicking on it lists the device contents.
No workaround needed.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma:  21.12.2
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 5.90.0
Qt Version: 

ADDITIONAL INFORMATION
https://forum.kde.org/viewtopic.php?f=225&t=168662&p=444513#p444513