There seem to be quite a few Roman amphitheatres that are in use today as bullrings, theatres and concert venues; are there any that have not seen a prolonged period of disuse at some point since the time they were built?
While not in constant use as an entertainment venue, the one in Nimes found other uses for at least most of its history. After gladitorial combat was outlawed it was fortified and used as a defensive refuge through into the Middle Ages, even being besieged on one occasion. That use then gave way to simple occupation: while the fabric was retained, the arena was filled in with houses, shops and two churches, so that there were 700 people living in it by the 18th century. There were apparently various attempts to clear these out over the years, but it wasn’t until about 1820 that these fully succeeded. Once the arena had been opened out again by that eviction and clearance, it quickly found a use as a venue for theatre and sports. It continues to be used in that way today.
But I suspect that there were still periods between these uses where it might have been sitting unused.