I changed the following in nextcloud/apps/documentserver_community/:
lib/Controller/StaticController.php (line 92):
} else if ($this->sessionManager->getSessionCount() >= 20) {
lib/XHRCommand/AuthCommand.php (line 37):
const MAX_CONNECTIONS = 20
If you also want to change the message:
js/sessionlimit.js:
OC.Notification.show(t("documentserver", "The community document server only supports up to 20 concurrent sessions"), {
Increasing the limits in these lines works for me. I’m not sure for what each of the occurences is exactly, but I just set both to the same high number.