Do you have an error that looks something like this in the activity log? (This example is for a backup to Google Drive – but the pattern can occur with various other remote storage methods too).

WP Time Capsule Error : (HTTP Code :28) Operation timed out after 25000 milliseconds with 0 out of -1 bytes received

This means that there was no network connectivity to the remote storage provider. (In the example above, it is saying that after 25000 milliseconds (i.e. 25 seconds), 0 bytes (i.e. absolutely zero) of data had been transported).

In this case, if the error persists (i.e. it happens again on a fresh try), you will want to talk to your web hosting provider, and show them the error, so that they can investigate. It is theoretically possible that the remote storage provider is temporarily having an outage – but, if it persists, then it’s far more likely that the network problem is at your web server's end, rather than at (for example) Google’s.

Note that WP Time Capsule is engineered to re-try if there is a network problem. Network problems happen often enough. You should wait at least half an hour before reporting the problem to anyone, to make sure that it is not just a one-off glitch.

In some cases, the problem is that the webserver has enabled IPv6 networking on the webserver (more information – Wikipedia), but with a broken setup. With IPv4 still dominating Internet traffic, this problem can sometimes pass for a long time on a server without being spotted. This is one possible cause of the above error. In this case, for Google storage (i.e. Google Drive or Google Cloud), you can find the following line, make it as true of your wp-content/plugins/wp-time-capsule/wptc-constants.php file, in order to cause WP Time Capsule to use IPv4 only:

$this->define( 'WPTC_GDRIVE_IPV4_ONLY', true);

If this does resolve the issue, then you should definitely report this to your web hosting provider, so that they can fix the misconfiguration on their server, which is better than just working around it in WP Time Capsule.