HA core 2026.6 caused X-Sense integration to stop working.
This one isn't a config problem on your side, it's a known break that's already fixed. The newer core tightened its "blocking call inside the event loop" check, and older X-Sense builds tripped it: the integration was creating its MQTT TLS context with ssl.create_default_context(), which loads the CA certs from disk (blocking I/O) during setup. Older cores only warned; the newer guard aborts it, so the integration fails to start.
The fix shipped shortly after 1.2.1. Update the X-Sense integration in HACS to the latest release (currently v1.2.6.3) and restart Home Assistant. The new code builds the TLS context in HA's executor instead of the event loop. If you're still on 1.2.1, that's the version with the bug.
If after updating you get a timeout ("Timed out connecting to X-Sense") instead of the blocking-call error, that's a separate, still-open issue (GH #190), not the core regression, so report there if it persists.
Details and the maintainer's fix note are in GH issue #188 on Jarnsen/ha-xsense-component_test.