X-Spam header missing regardless of low sa_tag_level_deflt but scores present in logs

[Bert Van de Poel]

Dear fellow Amavis users,

I recently migrated from a very old setup on Debian 8 to Debian 11. Both 
setups used Postfix with Amavis and Spamassassin, with Dovecot as the 
LDA. I've configured Amavis as I always do, to tag each and every email 
message with a spam score and status:
$sa_tag_level_deflt  = -9999;  # add spam info headers if at, or above 
that level
$sa_tag2_level_deflt = 5.0; # add 'spam detected' headers at that level
$sa_kill_level_deflt = 20; # triggers spam evasive actions
$sa_dsn_cutoff_level = 15;   # spam level beyond which a DSN is not sent
However, it seems that none of my messages are actually tagged in my 
inbox. I've not received any outright spam that scored above 5 (I only 
very recently migrated, and I reject/discard a lot of spam using the 
spamhaus blocklists in postfix), but regular email doesn't have the 
headers attached to it. I therefore initially suspected I had not 
configured things correctly and that amavis wasn't running properly. 
However, I do see very believable scores in my logs:
Aug 17 11:59:33 sys amavis[2337329]: (2337329-17) Passed CLEAN 
{RelayedOpenRelay}, [127.0.0.1] [40.107.20.101] 
<bert.vandepoel at uclouvain.be> -> <bert at bhack.net>, Message-ID: 
<8e22260c-6d20-86e4-d9e1-1a5d8a9632b9 at uclouvain.be>, mail_id: 
4EKz9ECqUE6T, Hits: 1.785, size: 8356, queued_as: 7C866BC40C, 3746 ms

Does anyone have any idea what I've done wrong or what I should be 
looking for?

I'm using amavis as a content filter in postfix.
main.cf:
content_filter = amavis:[127.0.0.1]:10024
master.cf:
127.0.0.1:10025 inet    n       -       -       -       - smtpd
         -o content_filter=
         -o local_recipient_maps=
         -o relay_recipient_maps=
         -o smtpd_restriction_classes=
         -o smtpd_client_restrictions=
         -o smtpd_helo_restrictions=
         -o smtpd_sender_restrictions=
         -o smtpd_recipient_restrictions=permit_mynetworks,reject
         -o mynetworks=127.0.0.0/8
         -o strict_rfc821_envelopes=yes
         -o 
receive_override_options=no_unknown_recipient_checks,no_header_body_checks
amavis     unix    -       -       -       -       2       smtp
         -o smtp_data_done_timeout=1200
         -o disable_dns_lookups=yes
If you need any further configuration to better understand my setup, 
then please let me know.

I hope someone can help me figure this out. It's getting quite 
frustrating since my setup now and my previous setup are very similar, 
yet the new one refuses to do what the previous one has always done 
perfectly.

Kind regards,
Bert Van de Poel