What is the ruling on the prayer of one who rises from bowing with the Imam or shortly after him? And is doing so disliked (makrooh) or forbidden (haraam)?

Your prayer is valid, because synchronizing with the Imam in bowing (rukūʿ) and prostration (sujūd) is reprehensible (makrūh), not prayer-invalidating, and doubt does not affect it. The basic principle is that a Prophetic prohibition entails prohibition (taḥrīm), but it may be shifted to reprehensibility (karāhah) if there is a diverting factor. Scholars have differed regarding the ruling on synchronizing with the Imam: some held it to be prohibited based on the apparent meaning of the prohibition, while most inclined towards reprehensibility, reasoning that the Prophetic strictness was directed at out-pacing the Imam, not synchronizing with him, and that synchronizing does not entirely negate following, unlike out-pacing.