I installed osTicket 1.16.1 on a computer on the network running CentOS7, MariaDB and initially with PHP 8.1. I installed the plugin that saves attachments to the file system. A cron job that fetches emails from one email account runs every 3 minutes.
That ran fine until I upgraded to 1.16.2 (could be a coincidence of course).

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After the upgrade I added an email by forwarding an email as an original to the account for osTicket and that was added as a ticket. Then I forwarded a reply to that email inserting the ticket number (sequential, not random) [#000054] in the subject string (as I did many times before without issue).
Then I found out I couldn't open the ticket (hovering over the link gives also an empty balloon). Just gives an empty page without page source. In the systemlog of osTicket no messages appear. The PHP error log is being filled with the same error message ever since:

[18-May-2022 07:48:01 UTC] PHP Fatal error:  Uncaught ObjectNotUnique: One object was expected; however multiple objects in the database matched the query. In fact, there are 2 matching objects. in /var/www/html/tickets/include/class.orm.php:1364
Stack trace:
#0 /var/www/html/tickets/include/class.orm.php(606): QuerySet->one()
#1 /var/www/html/tickets/include/class.model.php(66): VerySimpleModel::lookup(Array)
#2 /var/www/html/tickets/include/class.thread.php(81): ObjectModel::lookup(39, 'T')
#3 /var/www/html/tickets/include/class.thread.php(451): Thread->getObject()
#4 /var/www/html/tickets/include/class.thread.php(910): Thread->postEmail(Array, Object(ThreadEntry))
#5 /var/www/html/tickets/include/class.mailfetch.php(882): ThreadEntry->postEmail(Array)
#6 /var/www/html/tickets/include/class.mailfetch.php(955): MailFetcher->createTicket(1)
#7 /var/www/html/tickets/include/class.mailfetch.php(1035): MailFetcher->fetchEmails()
#8 /var/www/html/tickets/include/class.cron.php(25): MailFetcher::run()
#9 /var/www/html/tickets/include/class.cron.php(111): Cron::MailFetcher()
#10 /var/www/html/tickets/include/api.cron.php(19): Cron::run()
#11 /var/www/html/tickets/include/api.cron.php(40): CronApiController->run()
#12 /var/www/html/tickets/api/cron.php(23): LocalCronApiController::call()
#13 {main}
  thrown in /var/www/html/tickets/include/class.orm.php on line 1364

No other PHP errors are logged. This error appears in the log every 6 minutes whereas the cron job is every 3 minutes.

In the sql dump I made I can find the file that was attached to the last email as the last entry in the table ost_file but in the sql dump I cannot find any text from the email itself:

(154,'T','F','application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',15871,'Mb2oNyG-HbU650iVpEKi5YI80GqTBuPs','yG-HbU650iVpEKi5NuYTjLdUFFfb5sUz','BatchCode.xlsx',NULL,'2022-05-17 10:27:02')

That last email is not removed by osTicket. When I removed it manually from the mailbox and resend it nothing happens (the attachment is not added again). When I remove the email the errors from the cron job stop.

In the webserver logs similar errors about two matches appear:

[Wed May 18 09:39:24.022861 2022] [php:error] [pid 1561] [client 192.168.27.159:49245] PHP Fatal error: Uncaught ObjectNotUnique: One object was expected; however multiple objects in the database matched the query. In fact, there are 2 matching objects. in /var/www/html/tickets/include/class.orm.php:1364\nStack trace:\n#0 /var/www/html/tickets/include/class.orm.php(606): QuerySet->one()\n#1 /var/www/html/tickets/scp/tickets.php(36): VerySimpleModel::lookup(Array)\n#2 {main}\n thrown in /var/www/html/tickets/include/class.orm.php on line 1364, referer: http://192.168.27.164/tickets/scp/index.php
[Wed May 18 09:39:48.547196 2022] [php:error] [pid 1969] [client 192.168.27.159:49252] PHP Fatal error: Uncaught ObjectNotUnique: One object was expected; however multiple objects in the database matched the query. In fact, there are 2 matching objects. in /var/www/html/tickets/include/class.orm.php:1364\nStack trace:\n#0 /var/www/html/tickets/include/class.orm.php(606): QuerySet->one()\n#1 /var/www/html/tickets/include/ajax.tickets.php(243): VerySimpleModel::lookup(Array)\n#2 /var/www/html/tickets/include/class.dispatcher.php(145): TicketsAjaxAPI->previewTicket('39')\n#3 /var/www/html/tickets/include/class.dispatcher.php(38): UrlMatcher->dispatch('39/preview', Array)\n#4 /var/www/html/tickets/include/class.dispatcher.php(120): Dispatcher->resolve('39/preview', Array)\n#5 /var/www/html/tickets/include/class.dispatcher.php(38): UrlMatcher->dispatch('/tickets/39/pre...', NULL)\n#6 /var/www/html/tickets/scp/ajax.php(316): Dispatcher->resolve('/tickets/39/pre...')\n#7 {main}\n thrown in /var/www/html/tickets/include/class.orm.php on line 1364, referer: http://192.168.27.164/tickets/scp/index.php

Downgrading from PHP 8.1 to PHP 8.0.19 didn't help.
Deleting the ticket is not possible. I get an overlay that something is happening but that never goes away and the ticket is also not deleted.

I have no clue how to resolve this error. Thanks for any help.