Another thing of note: the car doesn't stay in high mode for long. It tries to rise up but the H light keeps flashing and it eventually comes back to normal height.
In addition to the conditions posted by
@flintknapper, also consider loads and hub-to-fender heights (Standard: Front 19.75 inches; Rear 20.50 inches -- measured with a tape measure).
More load = more AHC pressure,
More height = more AHC pressure,
Tired rear springs (replace) plus tired torsion bars (adjust) = more AHC pressure.
When AHC pressures are excessive, the system will refuse to raise and/or will sink. This is about the excessive load share carried by the AHC system and a requirement to transfer more load to the torsion bars and springs to get AHC pressures back into the correct range -- it is not about 'globe' condition. The FSM provides the following guidance on load limits at correct heights and correct AHC pressures:
Thinking about 'globes' -- Ideally you could check overall condition of the four 'globes' using the HI/LO Test -- recording the difference in graduations at the AHC Tank at "HI" and "LO" heights (14 graduations = as new; 7 graduations = replace 'globes' per FSM at correct AHC pressures -- BUT this test only works when the vehicle can be raised from "LO" to "HI". The outcome is only comparable with FSM recommendations when AHC pressures are correct.
It is vitally important to measure AHC pressures as part of the maintenance and monitoring of the system -- but be aware that AHC pressures alone tell nothing about the condition of the 'globes'.
Poor 'globe' condition certainly will result in poor ride quality.
In addition to advice in earlier replies and if not already seen, suggest have a look at the General Description of the AHC and TEMS systems at
https://lc100e.github.io/manual/
Go to tabs at Index Panel, top left of opening page -- New Car Features (first item in the list) > CHASSIS > Suspension > Active Height Control Suspension & Skyhook TEMS.
Then go through "The ABC's of AHC" thread assembled by
@LndXrsr mentioned at Post #2 above,
and,
view the video and "Cheat Sheet" provided by
@suprarx7nut at
AHC Basics for dummies Video re CrossLeveling, Height Sensor adjustment, TB tweaking - https://forum.ih8mud.com/threads/ahc-basics-for-dummies-video-re-crossleveling-height-sensor-adjustment-tb-tweaking.1225842/#post-13383401
DEFINITELY follow through on the diagnostic procedures using Techstream when your cable arrives. This can take a bit of effort to set up but good guidance can be found here:
Getting Techstream up and running can be a bit of a pain. Hopefully this helps someone get started quickly. Step 1: Purchase an OBD-II / Mini-VCI interface. - I have sold out of my cables and supply chains are back in order, so no reason to purchase more. Anything like this will work: Mini-VCI...
forum.ih8mud.com
This thread is lengthy but the early posts provide most of the required information.
Then suggest post a screenshot of your Techstream test data when you get to that point for more feedback.
The unknown blue fluid should be flushed out of the system as best possible as soon as possible and replaced with genuine (pink) Toyota/Lexus AHC Fluid. Wrong fluid may have caused unknown internal degradation, damage and formation of sludge, all impeding fluid flow within the system -- or you may be lucky!
Next after 'globes' (which are a wear item as mentioned by
@suprarx7nut) come the under-recognised problems caused by inadequately maintained and degraded Height Control Sensors.