Liking Instagram Post and Reel from different accounts and same device is Harmful or not?
It can actively hurt you.
Why it doesn't work:
Instagram's algorithm is sophisticated enough to detect engagement patterns. When multiple accounts engage with a post from the same device, same IP address, or in an unnaturally short time window, Instagram identifies it as artificial engagement and discounts those signals entirely. They don't count toward Stage 1 metrics.
Why it can hurt:
If Instagram detects coordinated fake engagement it doesn't just ignore it, it flags the post as potentially manipulated and reduces its organic distribution. The exact opposite of what you want during Stage 1.
At larger scale repeated artificial engagement signals can trigger a shadowban, where your content stops appearing on explore and hashtags without any notification. You'd be posting normally but reaching almost nobody outside your followers.
What Instagram looks for to detect it:
Same device or IP engaging from multiple accounts. Engagement happening within seconds of posting in an unnatural pattern. Accounts with low activity suddenly engaging heavily on one post.
What actually works instead:
Share the reel to your stories the moment it posts, that's the legitimate way to notify your most loyal followers immediately. A genuine share or mention there is legitimate cross-promotion and actually effective.
Send the reel directly to 5 to 10 people who you know will genuinely engage like friends, people who always watch your content. A real share to a real person who genuinely responds is worth more than 50 fake likes.
The algorithm is specifically built to find authentic engagement. Work with it not against it.