[The_Colonel]

All of these are legit, and that's why they're great excuses. CI works most of the time, but sometimes has hiccups for whatever reason. Everybody gets hit by such issues from time to time, this particular dev is just reeeally unlucky and happens to catch those every other day. But nobody keeps the stats. People might get a hunch something is wrong, but what can you do with that?

[pawelduda]

Offer help with troubleshooting, hop on a call (maybe pair programming), ask what have they tried to solve the problem, etc, etc... If you assume someone is slacking because of common roadblocks, you're setting yourself up for trust issues. If you see they are indeed underperforming, you can take regular steps from there. If they straight up lie it'll be obvious at some point. No need to start with stance of distrust IMO