If the problem happened soon after that Shop rebuilt the Carburetors, then most likely the problem is rooted in the Carbs.
They should not have changed any of the Jets. If the Needle Valves were replaced, thay should have used the same Size.
It's possible that the Shop used inferior Carb Rebuild Kits.
The Chinese Imitation Copy Cat Knock-Off Kits are cheap but do not meet Mikuni Specs. The Elastomers (Diaphragms) are inferior. The Imitation Regulator Diaphragms deform and leak after a short time. The Regulator Diaphragm Center Buttons are not the right size. That affects the Valve Needle position and movement, and thus Fuel Supply flow and response.
The Genuine Mikuni Regulator Diaphragm Center Buttons are Anodized Red. The Imitations are plain Metal with no anodizing color.
Call the Shop and ask them what brand Carb Rebuild Kit they used. Ask them to confirm if they were Genuine Mikuni Brand Kits.
Did the Shop install new Needle Valves too?
Must only use Genuine Authentic Made in Japan Mikuni SBN Carb Rebuild Kits.
Zip Tie the Fuel Supply Line to the Carb, it's missing. Zip tie the Pulse line ends too, as needed.