This was an upstream regression introduced in nginx 1.17.5. It is fixed in 1.17.7. Fixed by updating nginx to 1.17.7 in commit: 32dfde905229e593f9fe60795d2490f99c27aad5 and updating berlin config in maintenance on commit: 87d451e9c3381b21e6c7208372576abed84df1e6.
This is mentioned on then nginx 1.17.7 release notes as: Bugfix: a timeout might occur while handling pipelined requests in an SSL connection; the bug had appeared in 1.17.5. g_bor -- OpenPGP Key Fingerprint: 7988:3B9F:7D6A:4DBF:3719:0367:2506:A96C:CF63:0B21
