UFX+ (UFX II, 802, UFX) have a damping of the switch-on crackling on all outputs, not only phones.
I am not sure whether this could become "damaged" over time, this would be a question that only RME can answer.
To which outputs are your speakers connected ? To analog or digital outputs ?
I would definitively check the settings in TM FX, whether something changed there in terms of reference level (if you are using analog ports) and the output level.
I am not sure, whether stand-alone profiles of the UFX+ need to be checked as well if you turn on the UFX+ before the PC. From the manual its not 100% clear whether stand-alone mode is being entered with USB or Thunderbolt cable plugged, but computer turned off. Or whether the last loaded stand-alone profile is being loaded automatically or whether this needs to be done by the user every time manually.
Would also be a question to RME to clarify how this works and whether it would be worth to check levels (and reference levels) in stand-alone profiles.
Maybe its also worth to check, besides stores levels and reference levels in TM FX (also for normal operation, if computer is turned on), whether the recording interface is always properly initialized by TM FX on startup of the computer:
[x] Always init DSP devices with TotalMix FX settings
Just a few brainstormed ideas, but no idea, what the root-cause is.
Again pls, what monitors, connected to what ports ?
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14