I will say that most likely the previous owners caused the issues through neglected maintenance. I have not seen where the hybrid model can function properly without the AFM. That is my question. And the follow-up is, if I can't disable out, what is the best possible preventive maintenance?
I'm not familiar enough with the hybrid to know if it can work without the AFM. Sounds like it can't, and I'm sorry for this plight.
There really is no preventative maintenance other than normal maintenance. Since the AFM lifters are more sensitive to being clogged, the best you can do is keep the inside of the engine as clean as possible. Change your oil regularly/as needed using quality synthetic oils and filters, use top-tier gasoline, a good air filter, etc. Using additives to clean the engine such as the ones you pour in before an oil change and drive for X miles then drain can help. But, on an engine that already contains some sludge, the additive (detergents) can break the sludge/carbon loose and actually cause problems if chunks of the sludge get caught in the lifters. Since your engine has been worked on internally, I'd hope that it was cleaned decently enough that there aren't areas of buildup remaining, waiting to break loose and potentially cause a problem. If it's clean, keep it clean by running a quality cleaner somewhat regularly to prevent the buildup in the first place. Maybe run a bottle of cleaner before every or every other oil change.