I have a same problem:
# tail /usr/local/cwpsrv/logs/error_log
2020/01/17 20:38:11 [error] 10564#0: *43 FastCGI sent in stderr: "PHP message: PHP Fatal error: <br>The encoded file <b>/usr/local/cwpsrv/htdocs/admin/design/img/js.php</b> has expired. in Unknown on line 0" while reading response header from upstream, client: 1.2.3.4, server: localhost, request: "GET /cwp_37xxxxxxxxxxxxxxxx/admin/design/img/js.php HTTP/1.1", upstream: "fastcgi://unix:/usr/local/cwp/php71/var/sockets/cwpsrv.sock:", host: "sxxx.xxxxxxx.net:2031", referrer: "https://sxxxx.xxxxxxxxxx.net:2031/cwp_37xxxxxxxxx/admin/index.php?module=list_accounts"