You set up a comment-to-DM automation, it worked for the first few comments, and then your test comments stopped getting DMs - and they never even appear in your IGMsg activity log. Nine times out of ten, nothing is broken: Instagram's spam filter suppressed the comment before it ever reached IGMsg.
Understand what Instagram does with test comments
Instagram runs every comment through a spam filter before publishing it to the rest of the world. Repeated identical one-word comments (like the same keyword again and again), especially from new or low-activity accounts, are exactly what that filter targets. A suppressed comment is only visible to the account that wrote it - Instagram never registers it publicly and never generates a comment event for any app. Not for IGMsg, not for any other automation tool. That is why the comment shows on your screen but appears in no activity log anywhere.
Check whether your comment was suppressed
Open the post in an incognito/private browser window (or from an account that did not write the comment). If your test comment is not visible there, Instagram filtered it - the automation never had anything to react to. Comments that are visible publicly and contain your keyword will always reach your automation.
Test the way real customers comment
To test reliably: use an established Instagram account with normal activity history, vary the wording around your keyword (with the default contains match, "price please!" and "Price?" both trigger a keyword of price), and leave a few minutes between tests. Avoid posting the same single word from several fresh accounts in a row - that is the fastest way to get filtered.
Rule out the other common causes
If the comment IS publicly visible and still got no DM, check these in order: the automation is toggled Active and points at the right post; the comment actually matches your keywords and match mode; the commenter has not already received a DM from this automation (one DM per person per automation); and your plan's monthly DM limit is not reached - blocked sends always show a reason in your activity log.