Russian-speaking, I use Google Translator.
There are problems with the 500 error, installed Query Monitor, can you help with an explanation of what it is?
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator at [no address given] to inform them of the time this error occurred, and the actions you performed just before this error.
More information about this error may be available in the server error log.
Apache/2.4.25 (Debian) Server at globus-tours.com.ua Port 80
Screenshots issuing Query Monitor…
… with plugins:
http://prntscr.com/oqizla
http://prntscr.com/oqiztn
http://prntscr.com/oqj035
http://prntscr.com/oqj0f0
http://prntscr.com/oqj0qo
http://prntscr.com/oqj0wh
http://prntscr.com/oqj16m
http://prntscr.com/oqj1bo
http://prntscr.com/oqj1gd
http://prntscr.com/oqj2el
… without plugins (on test site):
Except Advanced Custom Fields (since the site is “made up of it”).
http://prntscr.com/oqj376
http://prntscr.com/oqj3dp
http://prntscr.com/oqj3k2
http://prntscr.com/oqj3tu
http://prntscr.com/oqj42d
http://prntscr.com/oqj48i
http://prntscr.com/oqj4g8
http://prntscr.com/oqj4l2
http://prntscr.com/oqj4pz
http://prntscr.com/oqj52c
Server logs ad debug on Google Drive.
Some errors from the log:
[Tue Jul 30 16:05:16.053090 2019] [fcgid:warn] [pid 24448] [client 66.249.66.93:46801] mod_fcgid: read data timeout in 31 seconds
[Tue Jul 30 16:05:16.166097 2019] [core:error] [pid 24448] [client 66.249.66.93:46801] End of script output before headers: index.php
[Mon Jul 29 17:34:29.961067 2019] [fcgid:warn] [pid 3764] [client 62.16.23.61:65353] mod_fcgid: read data timeout in 31 seconds, referer: http://globus-tours.com.ua/test_site_gt/wp-admin/plugins.php
[Mon Jul 29 17:34:29.961117 2019] [core:error] [pid 3764] [client 62.16.23.61:65353] End of script output before headers: admin-ajax.php, referer: http://globus-tours.com.ua/test_site_gt/wp-admin/plugins.php
[Mon Jul 29 22:07:09.721094 2019] [fcgid:warn] [pid 25806] [client 141.8.188.18:37735] mod_fcgid: read data timeout in 31 seconds
[Mon Jul 29 22:07:09.743195 2019] [core:error] [pid 25806] [client 141.8.188.18:37735] End of script output before headers: index.php
[Mon Jul 29 23:18:11.655298 2019] [fcgid:warn] [pid 1216] [client 162.208.50.90:43624] mod_fcgid: read data timeout in 31 seconds
[Mon Jul 29 23:18:11.911363 2019] [core:error] [pid 1216] [client 162.208.50.90:43624] End of script output before headers: index.php
[Mon Jul 29 17:13:06.173138 2019] [core:error] [pid 28002] [client 62.16.23.61:65266] End of script output before headers: admin-ajax.php, referer: http://globus-tours.com.ua/test_site_gt/wp-admin/admin.php?page=file-manager
[Mon Jul 29 17:14:59.489457 2019] [fcgid:warn] [pid 28857] (32)Broken pipe: [client 62.16.23.61:65272] mod_fcgid: ap_pass_brigade failed in handle_request_ipc function, referer: http://globus-tours.com.ua/test_site_gt/wp-admin/admin.php?page=file-manager
[Mon Jul 29 14:28:43.745669 2019] [fcgid:warn] [pid 1237] (104)Connection reset by peer: [client 194.0.131.145:40685] mod_fcgid: ap_pass_brigade failed in handle_request_ipc function