Does this sentence read well?
It is strongly recommended to also find out the reason as to why that happened.
I would suggest:
It is also strongly recommended to find out the reason [as to] why that happened.
("as to" is redundant as is "the reason")
But if you need to stress the point then you might expand a bit . . ."Also, it is strongly recommended to find out exactly why that happened."
However . . . "recommended" and the preposition "to" don't go together - you don't recommend to do something: you recommend that . . .
So it would be cleaner and more formal if you wrote (and now it comes closer to your original), "Also, it is strongly recommended that the reason for this event is discovered."
Better still . . . "Also, it is strongly recommended that the causes of this event are investigated." (Which is what needs to happen first before the reasons can be discovered!)