I submitted the 3rd and final revision of my manuscript last 3 weeks ago, however, it is not yet sent for review. I know that sometimes manuscripts take time to be reviewed but this one is quite strange for me. For the past 2 revisions, the paper was immediately sent for review. The last submission (R2) was only reviewed by the Associate Editor and has a very minor comment. I am hesitant to ask the Managing Editor about the progress of my manuscript. How long should I wait before I could email and ask the Managing Editor? Any advice.
3 weeks is sufficiently long to ask for an update, especially if precedent indicates the manuscript is sent for review "immediately".
I can't tell from your description who to approach, but presumably either the managing editor or the associate editor would be OK.