Arduino Pro Mini Serial.print issue

I am using this code (attached) on an Arduino Pro Mini for controlling a FPS and an OLED, which works fine.
But as soon as I insert a “Serial.print(“test”);” anywhere inside the loop function my FPS stops working plus nothing gets printed out to the serial monitor.

Any idea how to get this little “print test” working inside the loop?

Note: The FPS library uses SoftwareSerial on Pin 4 and 5. But debug prints of the FPS to the serial monitor are disabled so there should be no problems I guess

FPS_OLEDcode.ino (2.74 KB)