From personal experience and the documentation, there may be problems when mixing old and new access control directives in the configuration, e.g.
old:
Order deny,allow
Deny from all
# ...
new:
Require all denied
Mixing old directives like Order, Allow or Deny with new ones like Require is technically possible but discouraged. mod_access_compat was created to support configurations containing only old directives to facilitate the 2.4 upgrade. Please check the examples below to get a better idea about issues that might arise.
...
In the following example, mixing old and new directives leads to unexpected results.
I would like to convert to the new directives. It seems like a good idea to do this in one batch and then do a reload. However, some directives are in .htaccess files.
documentation:
I suggest to change the directives to something like this in your .htaccess files:
Example (you may want to check how the module is named on your system, e.g. mod_access_compat, access_compat_module):
Documentation: IfModule
The rest of the configuration can also be done this way or could be done in one batch with subsequent reload without the Ifmodules (in order not to clutter up the configuration).
Once the access_compat module is deactivated, the new directives will take effect.
Alternatively, you may want to think about moving the configuration from the .htaccess files to your webserver configuration, see:
https://httpd.apache.org/docs/2.4/howto/htaccess.html