Hello my friend. I have the same problem but i dont know where to change the ICACHE_RAM_ATTR void ISRfunction() {} instruction you say. Im using a ESP01 ESP8266 with WifiManager and Blynk. Everything was working fine; i did an upgrade and i think im now on ESP core 2.5.2.
Blynk keeps reconnecting with that ISR not in IRAM! error and i dont know where to fix it. Thanks