We are encountering various exceptions like

Exception: DateTime::__construct(): Failed to parse time string (-1-9-1) at position 4 (-): Double timezone specification

The specif error varies. I can not say when this exactly started. In addition, we encounter an ever rising amount of Submitting Data to IndexNow tasks.

Starting the cron script from the commandlien yields:

Exception:
Exception Object
(
    [message:protected] => Unknown or bad format (P-5D)
    [string:Exception:private] => 
    [code:protected] => 0
    [file:protected] => /srv/www/sites/forum/htdocs/applications/calendar/sources/Event/Event.php
    [line:protected] => 764
    [trace:Exception:private] => Array
        (
            [0] => Array
                (
                    [file] => /srv/www/sites/forum/htdocs/applications/calendar/sources/Event/Event.php
                    [line] => 764
                    [function] => __construct
                    [class] => DateInterval
                    [type] => ->
                )

            [1] => Array
                (
                    [file] => /srv/www/sites/forum/htdocs/applications/calendar/sources/Event/Event.php
                    [line] => 363
                    [function] => _findOccurances
                    [class] => IPS\calendar\_Event
                    [type] => ::
                )

            [2] => Array
                (
                    [file] => /srv/www/sites/forum/htdocs/applications/communitymap/extensions/communitymap/Mapmarkers/Calendar.php
                    [line] => 224
                    [function] => findOccurrences
                    [class] => IPS\calendar\_Event
                    [type] => ->
                )

            [3] => Array
                (
                    [file] => /srv/www/sites/forum/htdocs/applications/communitymap/extensions/core/Queue/RebuildCache.php
                    [line] => 119
                    [function] => getLocations
                    [class] => IPS\communitymap\extensions\communitymap\Mapmarkers\_Calendar
                    [type] => ->
                )

            [4] => Array
                (
                    [file] => /srv/www/sites/forum/htdocs/system/Task/Task.php
                    [line] => 47
                    [function] => run
                    [class] => IPS\communitymap\extensions\core\Queue\_RebuildCache
                    [type] => ->
                )

            [5] => Array
                (
                    [file] => /srv/www/sites/forum/htdocs/applications/core/tasks/queue.php
                    [line] => 43
                    [function] => runQueue
                    [class] => IPS\_Task
                    [type] => ::
                )

            [6] => Array
                (
                    [file] => /srv/www/sites/forum/htdocs/system/Task/Task.php
                    [line] => 375
                    [function] => IPS\core\tasks\{closure}
                    [class] => IPS\core\tasks\_queue
                    [type] => ->
                )

            [7] => Array
                (
                    [file] => /srv/www/sites/forum/htdocs/applications/core/tasks/queue.php
                    [line] => 55
                    [function] => runUntilTimeout
                    [class] => IPS\_Task
                    [type] => ->
                )

            [8] => Array
                (
                    [file] => /srv/www/sites/forum/htdocs/system/Task/Task.php
                    [line] => 274
                    [function] => execute
                    [class] => IPS\core\tasks\_queue
                    [type] => ->
                )

            [9] => Array
                (
                    [file] => /srv/www/sites/forum/htdocs/system/Task/Task.php
                    [line] => 237
                    [function] => run
                    [class] => IPS\_Task
                    [type] => ->
                )

            [10] => Array
                (
                    [file] => /srv/www/sites/forum/htdocs/applications/core/interface/task/task.php
                    [line] => 58
                    [function] => runAndLog
                    [class] => IPS\_Task
                    [type] => ->
                )

        )

    [previous:Exception:private] => 
)

As we are right in the middle of a planned migration, this is a real bummer - any help would be appreciated while we are searching for the reason ourselfes. Thank you!

I wonder if your host updated their PHP and did not include one of the required modules. 
 

Install that script and check to see if it says you’re missing a module.  If not, do these errors happen when all third party resources are disabled?

Besides the PHP-version check, everything is alright (as of the script). This happens on our current server (php 7.4) and out soon-to-be server (php 8.1).

It looks like we have been attacked - there are more than 3000 calendar entries with stuff in various fields that looks like SQL injection attacks and other garbage. I'll clean this up and we'll see if everything is fine again.

Please disable community map which looks to be extending calendar there. It looks like this may be what is causing you issues