AXFR Problems sind Upgrade to 9.16.12

[Klaus Darilion]

Hello!

Our setup: Customer Primary --> bind-1 --> bind-2 --> public secondaries (NSD/bind)

Today we upgraded bind-1 and bind-2 from: 
9.16.6-3+ubuntu18.04.1+isc+3   --->   9.16.12-2+ubuntu18.04.1+isc+1

AXFR from customer to bind-1 still works. But since the upgrade, bind-2 can not transfer the zone from bind-1 anymore:

bind-1[3591]: client @0x7f6090274c78 xx.xx.xx.20#42767/key rcode0-internal (example): transfer of 'example/IN': send: operation canceled
bind2[4699]: transfer of 'example/IN' from xx.xx.xx.22#53: failed while receiving responses: end of file
bind2[4699]: transfer of 'example/IN' from xx.xx.xx.22#53: Transfer status: end of file
bind2[4699]: transfer of 'example/IN' from xx.xx.xx.22#53: Transfer completed: 25079 messages, 9787583 records, 334058940 bytes, 30.171 secs (11072186 bytes/sec) (serial 1069865757)

I tried "dig axfr @bind-1 ..." which also fails:
;; communications error to xx.xx.xx.22#53: end of file

Same with kdig:
;; WARNING: can't connect to 83.136.34.24 at 53(TCP)
;; ERROR: failed to query server 83.136.34.24 at 53(TCP)

The AXFR fails after receiving ~ 400MB. The full zone would be ~600MB.

Of course also AXFR from bind-2 to our public secondaries fail to. So I suspect this is problem on the "sending" side of bind9. As it worked without problem until the upgrade I think this is a regression.

Are there any known issues with 9.16.12?
Do you provide old PPA packages so that we can downgrade?

Thanks
Klaus