AssertionError ("Deviation from expectations found") when using Infomaniak CalDAV with Home Assistant Container

[mamo79]

AssertionError ("Deviation from expectations found") when using Infomaniak CalDAV with Home Assistant Container

Description

Repeated AssertionError messages are logged by the caldav library when it is used as a module/integration under Home Assistant.[1]

The CalDAV backend is connected to an Infomaniak server, with multiple calendars and tasks enabled.[2][3]

Logs

Enregistreur: caldav
Source: /usr/local/lib/python3.14/site-packages/caldav/lib/error.py:53
S'est produit pour la première fois: 11 juin 2026 à 22:53:25 (104 occurrences)
Dernier enregistrement: 10:08:25

Deviation from expectations found. Please consider raising an issue at https://github.com/python-caldav/caldav/issues or reach out to t-caldav@tobixen.no, include this error and the traceback (if any) and tell what server you are using

Traceback (most recent call last):
  File "/usr/local/lib/python3.14/site-packages/caldav/lib/error.py", line 50, in assert_
    assert condition
AssertionError

Environment

• Installation method: Home Assistant Container
• Home Assistant Core: 2026.6.2
• Home Assistant frontend: 20260527.5
• Python: 3.14 (based on the module path in the traceback)
• Component: caldav
• Usage context: Home Assistant module / integration

CalDAV server

• Provider: Infomaniak
• Usage: multiple calendars and tasks[2][3]
• Possible endpoint family: https://sync.infomaniak.com[2][3]

Expected behavior

Normal calendar and task synchronization should not trigger assertion errors.

Actual behavior

The integration repeatedly logs:

Deviation from expectations found

with the traceback shown above.

Additional context

• First occurrence: 2026-06-11 22:53:25
• Last logged: 2026-06-12 10:08:25
• Number of occurrences: 104
• The traceback does not expose which internal condition failed.

[tobixen]

Infomaniac is new to me, I haven't tested it before. I see they have a "get started for free"-button, so I will have a look - but probably not today.

It's a bit strange to me that the asserts are enabled - they are supposed to be enabled in debug mode, only. Setting the environmental variable PYTHON_CALDAV_DEBUGMODE to PRODUCTION should cause the code to bypass the assertions.

[tobixen]

According to the guide, the URL to use for caldav connection is https://caldav.infomaniak.com - but caldav.infomaniak.com does not resolve. Any hints?

[mamo79]

I use sync.infomaniak.com on smartphone and other service.

[mamo79]

Maybe it's due to an annual repetitive task ?

[tobixen]

What I've found out so far (not much related to your problem though):

• The CalDAV support is based on SabreDAV, also used in Baikal, NextCloud, Davis and others - so it should have roughly the same set of compatibility-issues.
• The auto-discovery mechanisms in the caldav library does not work due to a server-side problem; the software naively assumes the login-username (the email I've provided) equals the principal username. Allegedly I should visit config.infomatik.com to find what CalDAV URLs to use.

I will continue researching this a bit later.