It looks like from the recording that t.MaxFPS was looked up in the console but not set, since it suggest it was last set by scalability. Would you be able to set t.MaxFPS first to 120, then to 60, both via the console?
Setting by the console will have a higher priority than by scalability, so this will help rule out things being stomped elsewhere. Setting to 120 first might also be necessary since it is already reporting 60, so going to 120 then to 60 will avoid any issues with it not setting it due to not being a new value. 120Hz is also the maximum refresh rate of the device, so this should be “valid”.
I’m also curious to know what kind of 5.5 engine build you are using. Is this a source build maintained by your team or an external team? It’s not out of the realm of possibility that there is some code tying max FPS to battery or temperature level, for instance.