I caught gpg-agent.exe hanging again and managed to attach WinDbg for live kernel debugging. Alas, the result is underwhelming, but I can now confirm with certainty, that the WOW64 loader lock and the fast PEB lock are not being held:

Sorry, I haven't been able to get any more information so far. I'll try to read up on the code a bit during my upcoming vacation, perhaps I can identify something. While I couldn't confirm that it's about the loader lock, but also couldn't rule it out.

Sorry for misleading you and others, perhaps. That particular thing happens to me time and time again. So if there are no symbols the stack symbols will use an offset relative to the nearest exported symbol. So my initial jumps to a conclusion were uncalled for in regards to the meaning of the stack.

In T6623#173512, @aheinecke wrote:

I also see this from time to time, mostly when the keyring is empty or very small. But never was able to reproduce it. I thought this might be fixed with keyboxd but if you say that scdaemon might be the culprit then I might misunderstood the issue and it is not the keyring loading that is stuck but maybe rather our configuration initialization which queries the config of each component and is also part of the "Loading certificate cache.."

The setting which I understood to be the workaround: