Hello,
That list comes from MQTT Explorer (Addon MQTT Explorer new Version).
Good luck finding your memory leak! I don’t have any pointers unfortunately, more than to mention that my (cpu increase, not memory though) was related to a LilyGo32 LoRa USB device which for some reason added all these MQTT entries. I deleted them all (through MQTT Explorer) and the cpu usage decreases significally. I have since stopped using this device.