Maybe not solved but a place to look.

The flasher relay is combined with the emergency flasher relay. This can be removed and there are six electrical pins on this box. You will need to test the function of each pin to see if it is passing current.

This is not difficult. Just time consuming.

To remove the relay from the dash unscrew the knob, unscrew the ferrel holding the switch/relay to the dash and remove it from behind the dash. Then just unplug it.

But check all your grounds. Clean the insides of each bulb socket. One bad ground can kill the entire system.

Also pull your fuses one by one and clean the contacts in the fuse holder. The fuse can be good but resistance builds up on the fuse box contacts and will prevent current from passing. This is easy to do and should be done every twenty or so years to prevent a weird electrical failure.