After upgrading the distro and then to php 7.3 the alert module works again.

Is this a known error? I guess I will try this, but first we have to update our distro.

All users who see this error (with debug mode), currently for CE you can update php to any version greater than 7.1!

We have the same issues after updating, the update itself was fine and it seems like only the alerts are broken.

Since we use observium to monitor our infrastructure and network this is a pretty bad thing, luckily we've got nagios to monitor our server-infrastructure so we're not totally in the dark.

This is the output from alerter.php:

mon2:/opt/observium# ./alerter.php -h host.domain.tld -dd
DEBUG!
DEFINITIONS loaded by: 0.0401499 ms

DEFINITIONS in memory: 15.9MB

SQL[PHP Parse error:  syntax error, unexpected '?', expecting variable (T_VARIABLE) in /opt/observium/libs/Doctrine/SqlFormatter/SqlFormatter.php on line 36

Parse error: syntax error, unexpected '?', expecting variable (T_VARIABLE) in /opt/observium/libs/Doctrine/SqlFormatter/SqlFormatter.php on line 36

Same Issue:

observium:/opt/observium# ./test_alert.php -a 7 -d -c 2
DEBUG!

CMD[/usr/bin/svn info /opt/observium]

CMD EXITCODE[0]
CMD RUNTIME[0.0216s]
CMD EXITDELAY[10ms]
STDOUT[
Path: .
Working Copy Root Path: /opt/observium
URL: http://svn.observium.org/svn/observium/branches/stable
Relative URL: ^/observium/branches/stable
Repository Root: http://svn.observium.org/svn
Repository UUID: 61d68cd4-352d-0410-923a-c4978735b2b8
Revision: 11812
Node Kind: directory
Schedule: normal
Last Changed Author: adama
Last Changed Rev: 11678
Last Changed Date: 2021-10-20 17:36:25 +0200 (Wed, 20 Oct 2021)

]
DEFINITIONS loaded by: 0.12201 ms

DEFINITIONS in memory: 13.5MB

SQL[PHP Parse error:  syntax error, unexpected '?', expecting variable (T_VARIABLE) in /opt/observium/libs/Doctrine/SqlFormatter/SqlFormatter.php on line 36

Parse error: syntax error, unexpected '?', expecting variable (T_VARIABLE) in /opt/observium/libs/Doctrine/SqlFormatter/SqlFormatter.php on line 36

This is a really hot topic because we do not receive alert emails anymore. And in this case we had a power failure on one switch without alerting 

In the immediate future: another problem,
I have just done the update; and during an alert test, I have the following error :

DEBUG!

CMD[/usr/bin/svn info /opt/observium]

CMD EXITCODE[0]
CMD RUNTIME[0.0164s]
CMD EXITDELAY[10ms]
STDOUT[
Path: .
Working Copy Root Path: /opt/observium
URL: http://svn.observium.org/svn/observium/branches/stable
Relative URL: ^/observium/branches/stable
Repository Root: http://svn.observium.org/svn
Repository UUID: 61d68cd4-352d-0410-923a-c4978735b2b8
Revision: 11679
Node Kind: directory
Schedule: normal
Last Changed Author: adama
Last Changed Rev: 11678
Last Changed Date: 2021-10-20 17:36:25 +0200 (Wed, 20 Oct 2021)

]
DEFINITIONS loaded by: 0.17976 ms

DEFINITIONS in memory: 13.6MB

SQL[PHP Parse error:  syntax error, unexpected '?', expecting variable (T_VARIABLE) in /opt/observium/libs/Doctrine/SqlFormatter/SqlFormatter.php on line 36

Parse error: syntax error, unexpected '?', expecting variable (T_VARIABLE) in /opt/observium/libs/Doctrine/SqlFormatter/SqlFormatter.php on line 36

This is very hard for detect why exactly you have troubles in common usage (and no problems with test alerts).

Can you provide temporary ssh access to your observium install (ie by tmate app: https://tmate.io/).
If possible, write me mail (mike@observium.org) or in discord channel: https://discord.gg/GjpNXKWm8W

the subject has not progressed
we still don't understand why the alert tests seem to be OK, but we still don't have any alerts from the equipment.
With one exception: alerts of dropped switch ports are reported to us - we have had problems on other equipment since then, but only some are reported to us.
We didn't change anything in our configuration before the upgrade, the alerts were working fine before.
We have this problem with every upgrade, usually it lasts a few hours/days, but this one has been going on for weeks.

You'll find the 2 test attached.
everything seems correct

Of course test needed when alerts don't receive.