SUMMARY
There is some "weirdness" with the hover tooltips on read receipt markers in the message timeline. These are technically two different manifestations, but they may stem from the same underlying cause.

1. No tooltip will be displayed on a receipt marker if no hover action buttons are being displayed for a message.

    STEPS TO REPRODUCE
    1. Find a room where there are read receipts in different places on the timeline.
    2. Position your cursor in a place on a marker where no hover action buttons are also displayed

    OBSERVED RESULT
    No hover tooltip appears for the read receipt markers.

    EXPECTED RESULT
    A hover tooltip to appear for the read receipt markers showing the display names of the users who have read the message.

2. In certain situations, the hover tooltip for read markers can rapidly change from visible to hidden. This one is a bit more tricky because I do not have a reliable way to reproduce the issue. I cannot get it to happen right now, but I'm fairly sure that when it happens, the hover actions for a message *also* flicker in and out simultaneously. It is this that causes me to think that these two issues may be one and the same.

    STEPS TO REPRODUCE
    1. Hover the mouse cursor over a read receipt

    OBSERVED RESULT
    The hover tooltip flickers in and out rapidly, making it impossible to see who has read a message.

    EXPECTED RESULT
    The hover tooltips for the read receipts should stay visible while the mouse cursor is hovered over it.

SOFTWARE/OS VERSIONS
Operating System: Solus 4.7
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.18.0
Qt Version: 6.9.2
Kernel Version: 6.16.5-322.current (64-bit)
Graphics Platform: Wayland
Processors: 24 × AMD Ryzen 9 5900X 12-Core Processor
Memory: 64 GiB of RAM (62.7 GiB usable)
Graphics Processor: AMD Radeon RX 6600

ADDITIONAL INFORMATION
Per redstrate on Matrix, this may be an issue with QtQuick tooltips.