Your game most likely isn't bugged.
While a space-time distortion is guaranteed to appear after 40 minutes, resting to a specific time of day will reset the timer that decides whether a distortion appears or not.
So, if you've been resting in camp until, say, the next morning over and over, then problem solved. Just rest for "a little while" instead.
If, however, you've been resting for a little while constantly for two hours and a distortion hasn't appeared, then I guess your game must be bugged... but let's hope it isn't.
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