Here are two lines of a tabular blast with an additional taxid-column:
gi|548452367|ref|XP_005675727.1|||1||abcL gi|1062853286|ref|XP_017907820.1| 100.000 15 0 0 1 15 483 497 1.28e-06 56.6 9925
gi|548452367|ref|XP_005675727.1|||1||abcL gi|942074311|ref|XP_005902399.2| 100.000 15 0 0 1 15 483 497 1.28e-06 56.6 72004
Actually, it seems that if the file ending does not have an expected blast file ending like ".tab", the parsing doesn't work; maybe this was the problem.
After some more trying I found that a tag like '|tax|9925' that is integrated into the subject id (like 'gi|1062853286|ref|XP_017907820.1|tax|9925') combined with a proper file ending works, so I'll go with this.
I still have one situation, in which a read should be assigned, but it's not. I'll send you the respective file by mail. Thank you.