His plan have been getting sidetracked for years.
?His plan have been being sidetracked for years.
The get-passive should not be confused with the main verb get followed by an adjective when it is used to mark a change of state.
Unfortunately, Lou got indisposed just before the big game.
Sometime the adjective is in the form of a past participle, which make it more difficult to distinguish main verb get from passive auxiliary verb get.
Unfortunately. Lou got indisposed just before the big game. (get is main verb followed by a past participle, which is an adjective)
We return to this point later in this chapter.