@KBExit Even more strange, no log entries about the problem, nothing.
Last logs
vendor/laminas/laminas-stratigility/src/Next.php(49): FoF\Terms\Middlewares\RegisterMiddleware->process()
/vendor/fof/oauth/src/Middleware/BindRequest.php(33): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): FoF\OAuth\Middleware\BindRequest->process()
/vendor/fof/oauth/src/Middleware/ErrorHandler.php(58): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): FoF\OAuth\Middleware\ErrorHandler->process()
/vendor/flarum/core/src/Http/Middleware/ContentTypeOptionsHeader.php(21): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\ContentTypeOptionsHeader->process()
/vendor/flarum/core/src/Http/Middleware/ReferrerPolicyHeader.php(30): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\ReferrerPolicyHeader->process()
/vendor/flarum/core/src/Http/Middleware/FlarumPromotionHeader.php(30): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\FlarumPromotionHeader->process()
/vendor/flarum/core/src/Http/Middleware/ShareErrorsFromSession.php(57): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\ShareErrorsFromSession->process()
/vendor/flarum/core/src/Http/Middleware/CheckCsrfToken.php(36): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\CheckCsrfToken->process()
/vendor/flarum/core/src/Http/Middleware/ResolveRoute.php(69): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\ResolveRoute->process()
/vendor/flarum/core/src/Http/Middleware/SetLocale.php(51): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\SetLocale->process()
/vendor/flarum/core/src/Http/Middleware/AuthenticateWithSession.php(31): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\AuthenticateWithSession->process()
/vendor/flarum/core/src/Http/Middleware/RememberFromCookie.php(63): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\RememberFromCookie->process()
/vendor/flarum/core/src/Http/Middleware/StartSession.php(61): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\StartSession->process()
/vendor/flarum/core/src/Http/Middleware/CollectGarbage.php(46): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\CollectGarbage->process()
/vendor/flarum/core/src/Http/Middleware/ParseJsonBody.php(28): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\ParseJsonBody->process()
/vendor/flarum/core/src/Http/Middleware/HandleErrors.php(57): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\HandleErrors->process()
/vendor/flarum/core/src/Http/Middleware/InjectActorReference.php(25): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\InjectActorReference->process()
/vendor/laminas/laminas-stratigility/src/MiddlewarePipe.php(81): Laminas\Stratigility\Next->handle()
/vendor/middlewares/request-handler/src/RequestHandler.php(84): Laminas\Stratigility\MiddlewarePipe->process()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Middlewares\RequestHandler->process()
/vendor/middlewares/base-path-router/src/BasePathRouter.php(97): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Middlewares\BasePathRouter->process()
/vendor/laminas/laminas-stratigility/src/Middleware/OriginalMessages.php(36): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Laminas\Stratigility\Middleware\OriginalMessages->process()
/vendor/middlewares/base-path/src/BasePath.php(73): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Middlewares\BasePath->process()
/vendor/flarum/core/src/Http/Middleware/ProcessIp.php(24): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/Next.php(49): Flarum\Http\Middleware\ProcessIp->process()
/vendor/laminas/laminas-stratigility/src/MiddlewarePipe.php(81): Laminas\Stratigility\Next->handle()
/vendor/laminas/laminas-stratigility/src/MiddlewarePipe.php(70): Laminas\Stratigility\MiddlewarePipe->process()
/vendor/laminas/laminas-httphandlerrunner/src/RequestHandlerRunner.php(73): Laminas\Stratigility\MiddlewarePipe->handle()
/vendor/flarum/core/src/Http/Server.php(45): Laminas\HttpHandlerRunner\RequestHandlerRunner->run()
/public/index.php(26): Flarum\Http\Server->listen()
#58 {main}
