Getting the same problem.
If I open the nginx log (/appdata/grocy/log/nginx) I get:
2019/05/11 19:56:40 [error] 299#299: *21 FastCGI sent in stderr: "PHP message: PHP Warning: file_put_contents(/app/grocy/data/viewcache/280834de7e8f30ba6d5b5ffd2e411299adf3057f.php): failed to open stream: No such file or directory in /app/grocy/vendor/illuminate/filesystem/Filesystem.php on line 122
PHP message: PHP Warning: include(/app/grocy/data/viewcache/280834de7e8f30ba6d5b5ffd2e411299adf3057f.php): failed to open stream: No such file or directory in /app/grocy/vendor/illuminate/view/Engines/PhpEngine.php on line 43
PHP message: PHP Warning: include(): Failed opening '/app/grocy/data/viewcache/280834de7e8f30ba6d5b5ffd2e411299adf3057f.php' for inclusion (include_path='.:/usr/share/php7') in /app/grocy/vendor/illuminate/view/Engines/PhpEngine.php on line 43" while reading response header from upstream, client: 192.168.0.191, server: _, request: "GET /login HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "192.168.0.10:9283"
2019/05/11 19:56:46 [error] 299#299: *17 FastCGI sent in stderr: "PHP message: PHP Warning: file_put_contents(/app/grocy/data/viewcache/280834de7e8f30ba6d5b5ffd2e411299adf3057f.php): failed to open stream: No such file or directory in /app/grocy/vendor/illuminate/filesystem/Filesystem.php on line 122
PHP message: PHP Warning: include(/app/grocy/data/viewcache/280834de7e8f30ba6d5b5ffd2e411299adf3057f.php): failed to open stream: No such file or directory in /app/grocy/vendor/illuminate/view/Engines/PhpEngine.php on line 43
PHP message: PHP Warning: include(): Failed opening '/app/grocy/data/viewcache/280834de7e8f30ba6d5b5ffd2e411299adf3057f.php' for inclusion (include_path='.:/usr/share/php7') in /app/grocy/vendor/illuminate/view/Engines/PhpEngine.php on line 43" while reading response header from upstream, client: 192.168.0.191, server: _, request: "GET /login HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "192.168.0.10:9283", referrer: "http://192.168.0.10/Docker"