All events disappear after subscribed calendar refresh

[jackmort37]

Hi,
Whenever I try to refresh a subscribed calendar (for example : https://mozorg.cdn.mozilla.net/media/caldata/FrenchHolidays.ics) all related events disappear.
On first import, evreything works perfectly. No error found in the log, even in debug levels.
Nothing relevant found in the log.
Is there a global debug variable to enable verbose logs to help track down the issue ?
Thanks.

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