Created attachment 128376 [details]
Serch dialogue with result and no hits

SUMMARY
Searching for e.g. "Important" messages will sometimes result in messages to be shown in the search dialogue, but at the bottom "0 matches" are stated (see attachment). Leaving the dialogue will show an empty search folder. The message is marked as "Important" and should be shown. Eventually (not after simply pressing F5, though), the message will be shown correctly even in the search folder.
Also, the message count of the search folder is not shown correctly. Even when a message is present in the messages list, the item count in the tool tip and folder list is "".
Behaviour seems to be triggered when using "Search in all folders", but also has been observed when using "Search only in"

Restarting kmail seems to solve the issue

STEPS TO REPRODUCE
1. create a new search
2. "Search in all folders"
3. "Message Status" is "Important"
4. Press "Search"
-> Message is shown, but "0 matches", search folder is empty
5. Switch to "Search only in" and select top level entry, with sub-folders
6. Press "Search"
-> Nothing changes
7. Press "Search" (why pressing twice is needed is unclear)
-> "1 match" is shown

OBSERVED RESULT
Unexpected and inconstant search result behaviour

EXPECTED RESULT
With any setting, the correct results should be shown

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.70.0
Qt Version: 5.14.2
Kernel Version: 5.6.11-arch1-1
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-4460 CPU @ 3.20GHz
Memory: 15,3 GiB