Crash while saving patients file

Good afternoon,

I am running openemr 7.0.2(1) on a Windows xampp installation with 16 GB RAM (only 5 used normally) and 8 possible CPUs in a virtual infrastructure. It is a teaching scenario.
When about 35 students work on a patients file and want to save it, openemr crashes with this error message:

PHP Fatal error: Uncaught TypeError: mysqli_query(): Argument #1 ($mysql) must be of type mysqli, bool given in C:\xampp2\htdocs\openemr\vendor\adodb\adodb-php\drivers\adodb-mysqli.inc.php:1370\nStack trace:\n#0 C:\xampp2\htdocs\openemr\vendor\adodb\adodb-php\drivers\adodb-mysqli.inc.php(1370): mysqli_query(false, 'SET NAMES ‘utf8…’, 0)\n#1 C:\xampp2\htdocs\openemr\vendor\adodb\adodb-php\adodb.inc.php(1613): ADODB_mysqli->_query('SET NAMES ‘utf8…’, false)\n#2 C:\xampp2\htdocs\openemr\vendor\adodb\adodb-php\drivers\adodb-mysqli.inc.php(1113): ADOConnection->_Execute('SET NAMES ‘utf8…’)\n#3 C:\xampp2\htdocs\openemr\src\Gacl\Gacl.php(189): ADODB_mysqli->execute('SET NAMES ‘utf8…’)\n#4 C:\xampp2\htdocs\openemr\src\Common\Acl\AclMain.php(133): OpenEMR\Gacl\Gacl->__construct()\n#5 C:\xampp2\htdocs\openemr\src\Common\Acl\AclMain.php(176): OpenEMR\Common\Acl\AclMain::collectGaclObject()\n#6 C:\xampp2\htdocs\openemr\src\Common\Acl\AclMain.php(170): OpenEMR\Common\Acl\AclMain::aclCheckCore(‘admin’, ‘super’, ‘Deadlock’)\n#7 C:\xampp2\htdocs\openemr\interface\patient_file\encounter\forms.php(540): OpenEMR\Common\Acl\AclMain::aclCheckCore(‘encounters’, ‘coding’, ‘Deadlock’, ‘write’)\n#8 C:\xampp2\htdocs\openemr\vendor\symfony\event-dispatcher\EventDispatcher.php(230): {closure}(Object(OpenEMR\Events\Encounter\EncounterMenuEvent), ‘menu.render’, Object(Symfony\Component\EventDispatcher\EventDispatcher))\n#9 C:\xampp2\htdocs\openemr\vendor\symfony\event-dispatcher\EventDispatcher.php(59): Symfony\Component\EventDispatcher\EventDispatcher->callListeners(Array, ‘menu.render’, Object(OpenEMR\Events\Encounter\EncounterMenuEvent))\n#10 C:\xampp2\htdocs\openemr\interface\patient_file\encounter\forms.php(614): Symfony\Component\EventDispatcher\EventDispatcher->dispatch(Object(OpenEMR\Events\Encounter\EncounterMenuEvent), ‘menu.render’)\n#11 {main}\n thrown in C:\xampp2\htdocs\openemr\vendor\adodb\adodb-php\drivers\adodb-mysqli.inc.php on line 1370, referer: https://openemr.th-deg.de/interface/patient_file/encounter/encounter_top.php

When fewer people work on the machine it´s load is also high, but it does not freeze.

I did all possible updates, increased hardware resources but I think it is a bug.
Can you please advise me, if I can do something myself?

Best Regards!
F.