FYI, ESP32 BLE & Blynk support is relatively new…
First off, as mentioned before, you have code running in the void loop()… trying to run thousands of times a second… which with the Blynk library is NOT recommended as it can interfere with the App/Server/Device communication required for IoT. Use timed functions for all your Serial and sensor routines.
Other than that, I don’t know, as I do not use BT or BLE with Blynk for any long term projects, just WiFi.