Describe the bug

Statistics for Sent mail are zero (0) for at least the past couple of weeks. I am not sure when the issue was first introduced.

To Reproduce
Steps to reproduce the behavior:

1. Go to ThirdStats Dashboard
2. Observe no stats for "Mails sent"
3. Try to rebuild cache
4. Observe no stats for "Mails sent" again

Expected behavior

Up-to-date and accurate statistics for Sent mail

Screenshots

System (please complete the following information):

• OS: Windows 10 Pro 20H2 x64 19042.1023
• Thunderbird Version: 90.0a1 (2021-05-30) (64-bit)

Additional context

• Isolation tests: rebuild cache. enable service workers (warning in dev console)

Developer Console messages: