Do the signals work fine when the parking lights are on ?
And just have problems when the headlights are on ?
That answer will determine where to start chasing gremlins ,
Also you should consider installing a relay harness for the headlights ,
Several places make them and they really help , it removes the electrical load from the dash and floor dimmer switch to a relay under the hood near the battery
It makes the lights a lot brighter too
Swap the old bulbs back in and see if that fixes it
Some vehicles just won’t work with LED bulbs
The side markers on the front , blink with the turn signal , and the blinking is opposite of the front signal,
When the front signal comes on , the side marker goes out , it’s done this way from the factory and it works somehow through the ground of the front signal . Installing LEDs in the front signal can mess this up somehow Because they don’t ground like an incandescent bulb
For the flasher , with LED bulbs , you will now need an “electronic “ flasher