Ok i figured it out.
Its only getting bugged from valor bard and only after lvl 5.
If i used 1d8 to improve my attack it was fine and working as intended.
But if i used it to improve my damage or improve my savings or my armor its bugged. I could fix it if i was long resting.
But if i try to inspire the same character agan the it became broken forever.
Also after lvl 5 the bonus for skill improve is unlimited and its not removing the inspired effect.
Yes, I'm getting bugged combat inspiration with my level 5 valour bard, too, and it looks as though the different handling of the valiant roll for skill checks vs the new reaction system for other effects might be at the root of the problem.
(a) If I "accidentally" apply combat inspiration twice to the same character, then the valiant roll toggleable passive remains, but all the new inspiration "reactions" vanish from the sheet (and don't seem to kick in auomatically when taking actions either), and I can't then apply combat inspiration to that character again until after a long rest.
(b) If a character with combat inspiration uses it to attack then it seems to work properly, and can be reapplied to the same character.
(c) But if the inspiration is used for damage or defence, then the reactions don't vanish from the tab, but instead show but with no bardic inspiration to fuel them so don't kick in. And reapplying combat inspiration just makes the reactions vanish and they then can't be reapplied. HOWEVER, the character still has combat inspiration showing on the tooltip, the glowy inspiration circle round the sprite and the valiant roll toggleable passive showing on their toolbar. And if valiant roll is then used for a skill check, I agree it doesn't vanish. This is fixed by long resting.
I couldn't manage to break combat inspiration in a way that couldn't be fixed by long resting, but perhaps I just didn't do exactly what ZOZO1006 did.
The bug at (a) seems to kick in before level 5 - or at least it happened on my level 4 character - but I agree (c) seems to work okay until level 5.
Btw, I'm not sure why the character given combat inspiration gets the musical note tab on their toolbar, given selecting it never seems to show any actions. Is that a holdover from the previous implementation before patch 9? I did play a bard once but can't recall if selecting it used to show the different toggle-able options. It does seem unnecessary to me now, given that an inspired character should have the icons confirming this at the top right of their toolbar and valiant roll shows in its own section of the toolbar.