Lightning, sync not working

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Nextcloud version (eg, 12.0.2): 15
Operating system and version (eg, Ubuntu 17.04): Kubuntu 18.04.2 LTS
Provider: Hostiso

The issue you are facing:

Connection seems to be working well; login as password. As a matter of facts, Thunderbird CardBox is being synchronized very well with contacts.
For calendar, all seems well, yet on the right side of the Nextcloud calendar in Lightning, a warning symbol appears, and when rolling the mouse pointer there, I get a message saying “Nextcloud momentarily not available”

The odd situation is, when I go to Nextcloud/Hostiso config to check activity on its access, in the list, I get:
" Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 Lightning/6.2.4 "
Seems to be connecting right? how come “Lightning” is doing nothing?

Android is syncing the Calendar very well via DAVx

Is this the first time you’ve seen this error? (Y/N): Yes

You might not have seen this posting which describes a Thunderbird/Lightning related problem, which has definitely been solved with Thunderbird 60.5.1/Lightning 6.5.2.1 (see https://github.com/nextcloud/server/issues/10134 for some background).

Thank you,

I just installed this version of Kubuntu in my PC, and maybe I’ll have to wait until Thunderbird is updated in Ubuntu repositories, with the new version 60.5.1