I've recently seen this using Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 on Ubuntu 18.04 LTS. It is intermittent, the item showing in the Today pane is Independence Day, and a restart of Thunderbird fixes the problem for me.
Bug 1583055 Comment 14 Edit History
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~~I've recently seen this using Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 on Ubuntu 18.04 LTS.~~ ~It is intermittent, the item showing in the Today pane is Independence Day, and a restart of Thunderbird fixes the problem for me.~~
~~I've recently seen this using Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 on Ubuntu 18.04 LTS.~~ ~It is intermittent, the item showing in the Today pane is Independence Day, and a restart of Thunderbird fixes the problem for me.~~ I was mistaken about being able to reproduce this on Linux. The problem is with TB 68.1.1 and Provider for Google Calendar 68.0 on Windows 10