Did you change anything in your PHP configuration?
Are you running the site under http or https? Did the url in $CFG->wwwroot in your config.php file change from https to http during the upgrade?
Disabling Slash Arguments is not a valid long term fix. You need to find and fix the undelrlying issue. If you use scorm packages in your courses you need Slash arguments to be enabled. And apparently Slash Arguments will one day be compulsory in Moodle, according to https://docs.moodle.org/38/en/Using_slash_arguments#Slash_arguments_environment_check.
Have you installed any non-core plugins? If you have then check that you've installed the latest version of those non-core plugins and that the latest versions of those are compatible with your new version of Moodle.
Lastly, check the permissions on your Moodledata directory and that Moodle / Apache has the correct read/write access to all the folders in Moodledata.
Have you installed any non-core plugins? If you have then check that you've installed the latest version of those non-core plugins and that the latest versions of those are compatible with your new version of Moodle.
Lastly, check the permissions on your Moodledata directory and that Moodle / Apache has the correct read/write access to all the folders in Moodledata.
Try the slash described in: https://moodle.org/mod/forum/discuss.php?d=346256#p1407611
Lastly, try deleting your Moodle config.php file again. The Moodleinstaller will recreate it again.