Fortigate-100E log in fail.

We have two Fortigate-100E installed, operating in HA A-P mode. Periodically, when trying to log in using the http protocol, it fails to log in to the system. At the same time, the following error appear when trying to log in: [size="1"]# [httpsd 8077 - 1635755401] ap_invoke_handler[571] -- new request (handler='logincheck-handler', uri='/logincheck', method='POST')[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[575] -- User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:45.0) Gecko/20100101 /[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[578] -- Source: 10.197.31.42:59957 Destination: 192.168.102.30:80[/size] [size="1"][httpsd 8077 - 1635755401] logincheck_handler[288] -- entering vdom for login_attempt (vdom='root')[/size] [size="1"][httpsd 8077 - 1635755401] logincheck_handler[322] -- login attempt OK, VDOM updated to 'root'[/size] [size="1"][httpsd 8077 - 1635755401] logincheck_handler[330] -- login_attempt (method=4, vdom='root', name='admin',admin_name='admin', rad_svr='')[/size] [size="1"][httpsd 8077 - 1635755401] output_response[45] -- sent response (status='1', buf='document.location="/ng/prompt?viewOnly&redir=%2Fng%2Fprompt%3FviewOnly%26redir%3D%252Fng%252Fprompt%253FviewOnly%2526redir%253D%25252Fng%25252Fprompt%25253FviewOnly%252526redir%25253D%2525252Fng%2525252F";[/size] ') [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[594] -- request completed (handler='logincheck-handler' result==0)[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[571] -- new request (handler='fortiweb-static-handler', uri='/ng/prompt?viewOnly&redir=%2Fng%2Fprompt%3FviewOnly%26redir%3D%252Fng%252Fprompt%253FviewOnly%2526redir%253D%25252Fng%25252Fprompt%25253FviewOnly%252526redir%25253D%2525252Fng%2525252F', method='GET')[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[575] -- User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:45.0) Gecko/20100101 /[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[578] -- Source: 10.197.31.42:59957 Destination: 192.168.102.30:80[/size] [size="1"][httpsd 8077 - 1635755401] add_nocache_headers[242] -- Added no-cache headers to /migadmin/ng/index.html[/size]

[size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[594] -- request completed (handler='fortiweb-static-handler' result==0)[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[571] -- new request (handler='fortiweb-static-handler', uri='/47cd8bea87902fb8621fb8aaee6b7e36/js/fweb_build.js', method='GET')[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[575] -- User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:45.0) Gecko/20100101 /[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[578] -- Source: 10.197.31.42:59957 Destination: 192.168.102.30:80[/size] [style="background-color: #ffff00;"][size="1"][httpsd 8077 - 1635755401] fortiweb_static_handler[289] -- Access denied: Not authorized to access the static resource file: /migadmin/js/fweb_build.js[/size][/style]

[size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[594] -- request completed (handler='fortiweb-static-handler' result==401)[/size] [size="1"][httpsd 8077 - 1635755401] ap_internal_redirect[1443] -- internal redirect to '/p/pubredir/httperror/'[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[571] -- new request (handler='fastcgi-script', uri='/p/pubredir/httperror/', method='GET')[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[575] -- User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:45.0) Gecko/20100101 /[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[578] -- Source: 10.197.31.42:59957 Destination: 192.168.102.30:80[/size] [size="1"][httpsd 18078 - 1635755401] aps_init_process_vdom[1200] -- initialized process vdom to 'root' (cookie='(null)')[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[594] -- request completed (handler='fastcgi-script' result==0)[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[571] -- new request (handler='login-handler', uri='/login?redir=%2Fng%2Fprompt%3FviewOnly%26redir%3D%252Fng%252Fprompt%253FviewOnly%2526redir%253D%25252Fng%25252Fprompt%25253FviewOnly%252526redir%25253D%2525252Fng%2525252Fprompt%2525253FviewOnly%25252526redir%2525253D%252525252Fng%252525252F', method='GET')[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[575] -- User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:45.0) Gecko/20100101 /[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[578] -- Source: 10.197.31.42:59957 Destination: 192.168.102.30:80[/size] [size="1"][httpsd 8077 - 1635755401] ap_invoke_handler[594] -- request completed (handler='login-handler' result==0).[/size]

It is possible to log in to the system only after rebooting the master device. But then this situation is repeated. What could be the reason for the failed login?