Here's a fun one. I hope this helps someone.
After upgrading to HA2026.7 (Container) I noticed one of my dashboards was incredibly slow, and even froze the browser on my mobile device. From looking at the new activity page, I tracked it down to a history graph card which had entities displaying information from Viseron sent via MQTT (mosquitto).
A little investigation of the two services showed that viseron was unable to keep a connection open to mosquitto and tried constantly to initiate a new connection, and mosquitto was refusing it because the packet size was too large. I remembered that as a part of the HA upgrade, mosquitto had been upgraded as well.
One I reconfigured mosquitto.conf to use max_packet_size 20000000 viseron could connect, and the dashboard now work without freezing or causing the browser to use 100% CPU.