So the passage is tucked away in the Finale movement of the symphony. I managed to find the notes for it in the Franz Schalk (1863-1931) score, pp. 136:
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It begins at around 54:30 in the Celibidache 1987 Munich recording and goes for about 30 seconds. It is taken up by the violins and the horns, in a call-response kind of pattern.
I wouldn't have thought anything much of it unless I hadn't happened to stumble into a church somewhere in Nuremberg on time, on holidays, and hear pretty much the exact same tune being played on the organ. I found it a bit odd that the organ was being played, as there didn't appear to be a service, and people seemed to be leaving.
I asked a friend about it and he said that in some catholic churches they play "ushering music". I wonder if such music is purely improvised, or whether there are actually specific pieces intended for this purpose, and whether these pieces might have either inspired, or been inspired by, Bruckner.
Or maybe I'm just obsessed with the music and hearings things! Haha
Anyway, keen to hear any information anyone has about this tune.