Why the Address Changes
A darknet market changes its onion address more often than a normal site changes its domain, and it is not confusion. The rotation is a feature, and understanding it is the difference between a bookmark that keeps working and one that dies the first time the set moves.
Why markets rotate
An address that is under attack can be abandoned. A new address starts clean. Rotation is how a market shrugs off a DDoS and a lookalike at the same time. It is also how it stays reachable when one entry point is saturated. The cost is that the set moves, and the buyers have to keep up.
What it means for you
A bookmarked address will stop working when the set rotates. That is expected, not a failure. The fix is to treat the directory, not the address, as the durable thing. Come back to the list, copy the current set, and the bookmark problem solves itself.
Staying current
Check the directory when you are about to use the market, not when you are already stuck on a dead address. A rotation is announced with a signed note, so if you see a note you have not seen, the set has moved and the old addresses are gone. Two minutes to re copy, and you are back in.