[imp] recent php 7.2.21 updates and updates of php-pear php-pecl php-http etc. cause Horde 5 Groupware Webmail edition (5.1.17 from debian repos) to stop working. Request advice

[info at interpost.biz]

Hello,  The August 8 and 9 2019 recent php 7.2.21 updates and updates of 
php-pear php-pecl php-http, etc. cause Horde 5 Groupware Webmail edition 
(5.1.17 from debian repos) to stop working. Request advice:

We had horde 5 groupware Webmail edition from debian stretch repos 
working fine on php7.2 until todays update:

[UPGRADE] libgd3:amd64 2.2.5-5.1+0~20190307222942.3+stretch~1.gbp1f9ff3 
-> 2.2.5-5.2+0~20190808.4+debian9~1.gbp6d9343
[UPGRADE] php-apcu-bc:amd64 
1.0.4-4+0~20190218103118.8+stretch~1.gbpa05194 -> 
1.0.5-1+0~20190808.9+debian9~1.gbp90a6a0
[UPGRADE] php-http:amd64 
3.2.0+2.6.0-2+0~20190219220936.5+stretch~1.gbp085e64 -> 
3.2.1+2.6.0-1+0~20190808.6+debian9~1.gbpbd8342
[UPGRADE] php-imagick:amd64 
3.4.3-4+0~20190217142022.9+stretch~1.gbpba1eeb -> 
3.4.4-1+0~20190808.10+debian9~1.gbpc5da26
[UPGRADE] php-pear:amd64 
1:1.10.8+submodules+notgz-1+0~20190219091011.9+stretch~1.gbp1a209a -> 
1:1.10.9+submodules+notgz-1+0~20190808.10+debian9~1.gbp296d25
[UPGRADE] php-pecl-http:amd64 
3.2.0+2.6.0-2+0~20190219220936.5+stretch~1.gbp085e64 -> 
3.2.1+2.6.0-1+0~20190808.6+debian9~1.gbpbd8342
[UPGRADE] php-redis:amd64 
4.3.0-1+0~20190606080331.12+stretch~1.gbp0171a6 -> 
5.0.2+4.3.0-2+0~20190809.14+debian9~1.gbp070358

We have disabled redis and php-redis and still have the same error on 
both a test and production server. (using roundcube to send this message 
:-))

  We have a login screen and we are setup to use imp to authenticate, and 
when we try to login we get a blank page with an error message stating 
that no data was sent and "ERR_EMPTY_RESPONSE" listed.  We did the 
php7.2 upgrades 2 days ago, and everything worked fine afterwards. It 
was only after the above upgrades that we can no longer login to any of 
the domains on the mails servers.

The only error in the logs (this server uses apache 2.4 latest ):

/usr/sbin/apache2: symbol lookup error: /usr/lib/php/20170718/http.so: 
undefined symbol: uidna_IDNToASCII

(could this error, combined with todays php-http update be causing the 
error? We are using the sury repos for stretch.

We are logging in at:  https://mail.example.com/horde/login.php and the 
return url is 
https://mail.example.com/horde/imp/dynamic.php?page=mailbox  (on ms edge 
  and chrome browsers) or 
https://mail.example.com/horde/imp/basic.php?mailbox=SU5CT1g&page=mailbox 
if we use "basic" login.

On Opera (for what it's worth) the behavior is even stranger: the login 
screen remains, the URL never changes, and the username-email address 
and the password disappear!

In the syslog we appear to have a valid login:

Aug 10 16:45:58 server1 dovecot: imap-login: Login: 
user=<info at example.com>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, 
mpid=9240, TLS, session=<qxVXWcSPauZ/AAAB>
Aug 10 16:45:58 server1 HORDE: [horde] Login success for 
info at example.com to horde (valid.ip.v.4) [pid 3057 on line 163 of 
"/usr/share/horde/login.php"]
Aug 10 16:45:58 server1 HORDE: [imp] Login success for info at example.com 
(valid.ip.v.4) to {imap://localhost/} [pid 3057 on line 156 of 
"/usr/share/horde/imp/lib/Auth.php"]
Aug 10 16:45:58 server1 dovecot: imap(info at example.com): Logged out 
in=124 out=825
Aug 10 16:45:59 server1 dovecot: imap-login: Login: 
user=<info at example.com>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, 
mpid=9242, TLS, session=<Sk5hWcSPbOZ/AAAB>
Aug 10 16:45:59 server1 dovecot: imap(info at example.com): Connection 
closed in=302 out=17126
Aug 10 16:46:00 server1 dovecot: imap-login: Login: 
user=<info at example.com>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, 
mpid=9244, TLS, session=<sttvWcSPbuZ/AAAB>
Aug 10 16:46:00 server1 dovecot: imap(info at example.com): Connection 
closed in=302 out=17118

So, it appears to be working but we can't see anything on any browser, 
except the login screen.

I realize that you don't officially support php7.2 yet (you should and 
7.3 for performance and because everything below 7.2 is slowly being 
deprecated), but can you give any advice about where to solve this error 
without installing and using php7.1.

Any help greatly appreciated.

Best,

Ed