I have a floating toolbar that I enable and disable with a hotkey: Toolbar NAME="Floating Toolbar" STATE=float APPBAR=top POS=mousel TOGGLE AUTOCLOSE
As of 13.9 when I invoke it all of the icons take a split second to load. It happens on several machines and configs so I know it's a bug and not my install.
Opus 12 used to make you wait for the icons to load before the toolbar appeared at all.
Opus 13 shows placeholders while the icons load in the background.
The icons appear in a similar amount of time in both cases, but you can see and use the toolbar in Opus 13 if an icon is taking a long time to come back (e.g. a button using an icon on a network drive that isn't on the network).
AFAIK 13.9 didn't change anything related. The 13.9.1 beta after it did have a related change, however.
It's strange because that delay happened either with 13.8 or 13.9. I'm not sure which because 13.9 came so quickly. I'll try the beta and see if that fixes it and report back.
We've made a change for 13.9.3 which should make the flicker much quicker (or possibly even not visible at all) the second and subsequent times the toolbar is opened.