Thanks Marc Schipperheyn for all these follow up comments. I try to reply to a few:

yeah, I also considered the ignoreAnalyzer on a non analyzed field the most likely candidate and I therefore removed all those, with the exact same result.

well, actually I meant ignoreFieldBridge() which is why it works if you add it. That's the setting which converts potential non strings in the matching clause via the field bridges.

In any case, it seems to occur in IndexedEmbedded classes that are not @Indexed themselves and where the @Field has index= Index.YES,analyze=Analyze.NO attributes.

Is that still the latest summary? Is this what I should try to setup?

If I use .ignoreFieldBridge(), it works. But that should not be necessary.

See, I am not so sure about that, but I need to dig a bit deeper here.

I think that what we have here is in some cases, some of the metadata for embedded fields either doesn't properly initialized or gets overwritten. I'm still trying to get a handle on when this might occur.

This might explain why I have problems reproducing the problem. Btw, which OS and Java version are you using?