Next you can ask aunt G. for help. Although the following blog post is in German language you should be able to read it using e.g. Google translator. I think it describes your problem, which is mainly caused by an iOS software change, and might help you understanding/fixing the problem:
I also found this thread in English language in the Apple forum:
Yep, @j-ed, I already take a look before posts. Unfortunatly none of the proposed solutions worked.
To be clear, my problem is not related to iOS, itâs about Mac OS.
I tested with several other calDav solutions (radical/mailu/,fruux, etc.), none of them work.
I suppose a SSL problem. But I canât figure out if itâs only that.
Based on the cited German blog post, the problem appears on both systems, iOS AND MacOS. The article indeed refers to a certificate issue:
Apple has straightened there certificate policy for server certificates on iOS 13 and macOS 10.15. A certificate need to fullfil the following requirements to be accepted:
The certificate key length need to be at least 2048 bits.
The certificate need to be signed with a SHA-2 certificate key.
The DNS name of the server need to be part of the SAN extension of the certificate (It isnât allowed to put the DNS name in the CommonName field - I personally donât believe that)
For certificates which have been created after September 1st 2019 this requirement is also needed:
The certificate need to contain an EKU extension with id-kp-serverAuth OID.
(Donât aks me what this is)
I have the same issue. Calendar and Tasks sync without issue on iOS 14.2. On macOS 11.0.1 (Big Sur), Calendar syncs, but tasks do not. It worked fine on Catalina.
Iâm having the exact same issue as psychotic. Everything was working fine on Catalina, everything still works fine on iOS 14, but in Big Sur only Calendar will sync, Reminders wonât update at all.
Instead of using the Cloudflare SSL certificate, I have tried with a letâs encrypt.
This way, it works on iOS, but still not on MacOS Reminders.app
There must be a bug in the application (Reminders.app), or they stopped supporting CalDAV, because I have tested with several CalDAV providers/solutions, without success.
Iâm also pretty sure that this is not a certificate issue and we mixing up two things here.
The problem described by j-ed was indeed through the upgrade to catalina as Apple changed the allowed connections.
Now, I think we face a new issue. I have the same problem as Heziode.
The syncronization works well on iOS 14 (contacts, reminders and calender) and also on Mac OS Big Sur but only for calendar and contacts. As described, the reminders app shows the headline of the servername but doesnât sync the reminders.
(The weird thing is: during the first setup all tasks were synced one time with Big Sur. But suddenly the syncing stopped and as I deleted and readded the CalDav-Account, reminders doesnât show up at all)
So to be clear again. This is not an iOS issue and not the same certificate issue as it was during the upgrade to Mac OS Catalina. Iâm using Letâs Ecnrypt certificates without any problems.
No ideas for now. I think the same issue is described in this post:
I have just called the telephone support, explained the problem to the assistant. After a while, it understand that this problem is beyond its competences, so it transmits to itâs ân+1â, re-explain the problem, and the ân+1â understand that the problem is probably a bug. So it create a ticket for there engineer team.
today I have a nearly 2h call with the Apple support. We figured out, that the sync work if I start my Mac in Secure Mode (start with pressed Shift key). The conclution was that some application block the connection.
After the call I tried a few things and found out that my issue was caused by Little Snitch (5.0.4). When I disable the Little Snitch network adapter in system preferences the sync work also in normal Mode. I wrote the Little Snitch support. I will report here when I got an answerâŠ
After reading your post, I also tried starting up with Shift held, and sure enough, it works. However, I donât have Little Snitch installed. I do have the Cisco AnyConnect VPN client installed though, and after removing that, it started working fine.
I wonder if there is still a bug at the OS level that causes it not to function when any network filter driver is installed.
Hi psychotic! I still have no feedback from the Little Snitch support. I will send them your info! Hopefully they have a better relationship with the Apple Devs/Support than I do. Donât want to spent 2 more hours exlaining it some low level supporterâŠ
Hi all! I got info from the Little Snitch support. They reported and/or follow other bugreports of the problem related to âThird-Party Network Extensions and Cloud Servicesâ at Apple. Hope Apple take care of the problem soonâŠ
I didnât try the secure mode, but after the description of you two I could guess some network issue. As Iâm not using any of your tools, Iâm using TripMode (which blocks network traffic during mobile connections). The TripMode network adapter seems to be active all the time even if the program is not running.
After deactivating this adapter in the network seetings, the tasks are synchronising.
Since TripMode isnât that important for me currently, I will leave it deactivated for now.
Thank you again for your contribution and your effort calling the apple support as this has a big influence on my daily workflow
Since disabling Little Snitch is not a real solution, I do not mark the subject solved for now.
I stay tuned for a working update of MacOS / Little Snitch that fix this issue.
