Hi! today, in three different sites trying to upgrade from 3.6.10 to 3.8.2 I got an extrange error message No Reason Phrase see No Reason Phrase.png
To do the upgrade I drop the files in the joomla installer screen
Upgrading time take long, but it won't fail upgrading other extensions like SP Page Builder, Akeeba Pro, JCE Pro, RO CSVI and so on, all using joomla installer
After that no reason phrase error, VM page says it's 3.8.2 but I doubt that database upgrade took place, so I enable database tools and try to do a "Install/upgrade database tables" but I get 524 A timeout occurred (see screenshot)
My joomla version is 3.9.21 over Apache, PHP 7.3.21, linux, MySQL, etc
Perhaps discuss the 524 error in the cloudflare community. Background Error 524 error indicates that Cloudflare made a successful TCP connection to the origin web server, but the origin did not reply with an HTTP response before the connection timed out. ... If the origin doesn't respond in that time, Cloudflare closes the connection and you'll see "Error 524: A timeout occurred".
I remember one case where using php 7.2 or 7.3 instead of php 7.4 solved it. Maybe not all of your extensions/modules are happy with 7.4 (in case you do use it).