Failure Code with PublishPress Authors

Dear team,

recently my host (raidboxes) installed the latest wordpress update. (full-service plan) Since than I am not able to create new posts with the plugin “PublishPress Authors” activated. So I am not able to set guest authors which I need for my blog. I already contacted the hosting support who gave me this failure code:

Uncaught Error: Call to a member function get_avatar_url() on bool in /home/wp/disk/wordpress/wp-content/plugins/publishpress-authors/src/modules/rest-api/rest-api.php:140#6 /home/wp/disk/wordpress/wp-includes/r” while reading response header from upstream, client: 170.82.204.108, server: casamiracles.com, request: “GET /wp-admin/post.php?post=705&action=edit HTTP/2.0”, upstream: “fastcgi://unix:/var/run/wordpress.php-fpm.sock:”, host: “casamiracles.com”, referrer: “https://casamiracles.com/?p=705&preview=true”#5 /home/wp/disk/wordpress/wp-includes/rest-api.php(519): WP_REST_Server->dispatch()#4 /home/wp/disk/wordpress/wp-includes/rest-api/class-wp-rest-server.php(990): WP_REST_Server->respond_to_request()#3 /home/wp/disk/wordpress/wp-includes/rest-api/class-wp-rest-server.php(1143): WP_REST_Posts_Controller->get_item()#2 /home/wp/disk/wordpress/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php(560): WP_REST_Posts_Controller->prepare_item_for_response()#1 /home/wp/disk/wordpress/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php(1923): WP_REST_Controller->add_additional_fields_to_object()#0 /home/wp/disk/wordpress/wp-includes/rest-api/endpoints/class-wp-rest-controller.php(433): MA_REST_API->getPostAuthorsCallBack()

Also every time I try to create a new post I get a window coming up and also a mail with a possibility to try to solve it in the recovery mode. In the recovery mode there is no problem. I saw if its really due to the update by cloning the hostingbox with the old wordpress version (from just a day ago). If I clone it there is no problem and everything works smoothly… Can someone help me and tell me what the problem is? It would be amazing to get the plugin running again without loosing my guest authors and setup. Is it a common problem with the new version of wordpress?