Gmail not loading issue occurs due to many reasons. Some of the reasons are as follows:
1) First of all, you are using an improper Internet connection.
2) Working on an outdated version of the web browser.
3) Gmail IMAP and SMTP Settings are not working properly.
4) Plugins are not actively responding.
5) Storage limit is full.
These are the reasons which lead to Gmail not loading issue. Here you can learn how to fix this issue.
Gmail Not Working? Learn How Can You Fix It
Learn how to fix Gmail not loading issue in an easy way.
https://www.emailtechnicalsupport.us/blog/gmail-not-working/