While Peter Kämpf has addressed the L-55's case, the question asks about loss of lift accidents in general, and the loss of the USS Macon (ZRS-5) provides an additional perspective.
As mentioned elsewhere, rigid airships flew with the lifting gas at the ambient pressure: their lifting cells within the envelope were only partially inflated on the ground, and as the craft gained altitude, they expanded. If they reached their full extent, any additional gain of altitude beyond this ‘pressure height’ would lead to gas being released through safety valves, in order to avoid an overpressure that could rupture a cell.
The demise of the Macon started with the failure of the incompletely-repaired upper fin, which punctured one or more of the rear gas cells. The officer-in-charge’s response was to drop large quantities of ballast and fuel, causing the ship to zoom well above its pressure height, which was less than 3000 ft., leading to an additional loss of gas. This climb was exacerbated by the change in pitch resulting from the loss of gas from the rear cells, which was not fully compensated for by the elevator man, and which produced additional dynamic lift.
As pointed out by Peter Kämpf, venting gas from exceeding the pressure height is not generally sufficient to leave the ship deficient in buoyancy: given that the amount of gas remaining is sufficient to support it at this altitude, it is sufficient to support it at any lower altitude, so long as the gas is no colder than the surrounding air. This is a consequence of the ideal gas law (and the fact that hydrogen, helium and air are all very nearly ideal gases at atmospheric pressures and temperatures): a mole of one gas will displace a mole of another if they are at the same pressure and temperature, regardless of what that temperature and pressure is, and so, by Archimedes’ principle, will create a similarly-independent buoyancy equal to the weight of one mole of the displaced gas.
In the Macon’s case, however, losing additional gas would not have helped in dealing with the leakage from the punctured cells, and some forty minutes later, it settled on the water. It is the opinion of historian Richard K. Smith that the excursion above the pressure height was decisive, and without the additional loss of lifting capacity that it caused, the Macon may well have remained airborne. He believes that mishandling of the ship led to dynamic lift contributing to the zoom, in which case the above analysis is not necessarily sufficient, as in the presence of dynamic lift (or upwards momentum), we cannot assume the ship was buoyant above the pressure height.
This is essentially the mirror image of Peter Kämpf's argument: if the airship did not contain sufficient gas to be statically buoyant at the apex of its trajectory, then it did not contain sufficient gas to be so at any lower altitude, a situation that could only be remedied through dynamic lift or by jettisoning weight - something the crew was working on until almost the last minute. Once it became apparent that a crash was likely, the commander had to confront the choice between slowing down or endangering everyone on board, with the former robbing the craft of dynamic lift.
In the case of the L-55, launching with its cells only one-third filled, the pressure height would have been about or perhaps a little above its record-breaking altitude, where the density is about one third of that at sea level. The pressure height of an airship is not fixed in construction, but by the degree to which it is filled before launch.