SB PRO drivers are a headache even with real hardware somehow. Windows 3.1 integrated Sound Blaster 1.5 drivers are rock solid even with clone cards. Sound Blaster 16 drivers are hard to set up but ok to use. But somehow Sound Blaster PRO 1.0 drivers do not exist. And Sound Blaster PRO 2.0 drivers are buggy/picky. Maybe someone can shed a light to that. Even Windows 3.00 Multimedia Version has better Sound Blaster drivers.

I think same. There are a few at vogonsdrivers.com as well.

What's notable about this time frame is that the SB 1.x, 2.x and Pro models had been supported by ordinary, old Windows 3.0 already.
The earliest SB drivers were shipped as a simple DLL file (sndblst.dll), which only a few applications had supported.

After Windows 3.0 MME or 3.1 was released, it had been abandoned.
Creative disencouraged to use that DLL in further application releases.

So there was a switch of some kind happening. From sndblst.dll to real Windows drivers.
Maybe that also was a time of re-writes of Sound Blaster drivers, resulting in bugs or stability issues.

Considering that the SB Pro was the flag-ship model during the trasitional time, the most complex model with a shortlived mixer chip,
it might explain why its driver was most buggy.

But that's just an idea.

There also were builds of Windows 3.0 MME that shipped with SB Pro drivers..
If they work stable, maybe Windows 3.1 can be installed as an upgrade over 3.0 MME?

Yes Windows 3.00 MMW sound drivers can be used in 3.1. Have not used them long enough to notice any critical failure or bug.

I don't know about 86box, but SBP2WU.EXE worked fine for me in DOSBox.

Eh? Never had issues with Win 3.1 SBPro driver install. IIRC you install it in DOS first, then go to the WIN folder inside the SBPRO directory on your HDD and run the exe in there from within Windows.