I'm having the same performance issue with the latest versions: haxelib list
firetongue: [git]
flixel-addons: [2.7.1]
flixel-tools: [1.4.2]
flixel-ui: [2.3.1]
flixel: [4.5.1]
hscript: [2.3.0]
hxcpp: [4.0.4]
lime: [7.1.1]
openfl: [8.6.4]
systools: [1.1.0]

Everything is ok if I downgrade...

I also checked that http://haxeflixel.com/demos/ProjectJumper/ has the same performance issue.