People can’t register after deleting a profile field

I had a field used in the registration screen. Deleted the field and now the registration is broken:

SELECT * FROM `core_pfields_content` WHERE member_id = IS NULL
IPS\Db\Exception: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'IS NULL' at line 1 (1064)
#0 /home/sosinvisioncom/public_html/system/Db/Select.php(402): IPS\Db->preparedQuery()
#1 /home/sosinvisioncom/public_html/system/Db/Select.php(460): IPS\Db\Select->runQuery()
#2 /home/sosinvisioncom/public_html/system/Db/Select.php(384): IPS\Db\Select->rewind()
#3 /home/sosinvisioncom/public_html/applications/core/extensions/core/ProfileSteps/ProfileFields.php(250): IPS\Db\Select->first()
#4 /home/sosinvisioncom/public_html/applications/core/modules/front/system/register.php(257): IPS\core\extensions\core\ProfileSteps\ProfileFields::wizard()
#5 /home/sosinvisioncom/public_html/system/Dispatcher/Controller.php(139): IPS\core\modules\front\system\register->manage()
#6 /home/sosinvisioncom/public_html/system/Dispatcher/Dispatcher.php(169): IPS\Dispatcher\Controller->execute()
#7 /home/sosinvisioncom/public_html/index.php(16): IPS\Dispatcher->run()
#8 {main}

So I switched from the full registration to quick registration, now another error pops up: EX0:

Error: Attempt to assign property "class" on array (0)
#0 /home/sosinvisioncom/public_html/system/Dispatcher/Controller.php(139): IPS\core\modules\front\system\register->manage()
#1 /home/sosinvisioncom/public_html/system/Dispatcher/Dispatcher.php(169): IPS\Dispatcher\Controller->execute()
#2 /home/sosinvisioncom/public_html/index.php(16): IPS\Dispatcher->run()
#3 {main}

I had to disable the registration.