The flash rate of the older turn signal flashers is deliberately load sensitive.
It's a design feature... I remember my mom's '57 Cadillac owners manual specifically saying that the flasher was designed to "speed up" just to let you know when a bulb burned out... I later found out it's an inherent side effect of the low-cost design. I was 8 years old when I "helped" my dad change a burned out turn signal bulb...
Incandescent bulbs draw an amp or so each, the LED bulbs draw about 1/10 or so each. So with a bulb on the front fender and another on the rear fender, that's a load of about a couple of amps. My MH uses two rear lamps per side, so that's 3 bulbs. It also has a different flasher for the emergency flashers, as that's a load of 6 bulbs.
Most LED conversion kits offer "ballast resistors" or "load resistors". All they do is get hot while they pretend to be the incandescent bulbs that the LEDs replaced.
When I went to LED bulbs in my MH (and also converted the side marker lights into markers and turn signals) I went to the local NAPA store and asked for a flasher that was independent of load. I didn't want load resistors getting hot under my dash or inside my end caps. I knew they existed as they were designed back in the 1980s originally for tractor-trailer rigs... a tractor might be driving down the road with no trailers or one or two (and in some states, like Oregon, three) trailers, each with their own turn signal bulbs. I think Australia allows five, maybe six trailers... they call them "trailer trains".
As i was typing this I just now looked at amazon and found this one. It looks like what NAPA sold me: https: // www.amazon.com/Replacement-Adjustable-Compatible-Electronic-MOTORCYCLE/dp/B07D33JGLC
Yes, it says motorcycle but if you have a two pin flasher with the pins at right angle and the same spacing it should work.
For more information just google "load independent turn signal flasher" (without the quotes). There are a number of them out there.