Many bulbs are susceptible to fungus bulb rot, a pathogen found naturally in many soils. Last year was an unusually wet year with frequent rains. Clay soils would tend to dry out slowly. As temperatures rise, and in the presence of fertilizer, fungus bulb rot could spread throughout a bed, destroying all remaining bulbs. Again, one cultivar might be more resistant to bulb rot than another, explaining why one bed declined while another bed continues to perform.
Rodents sometimes destroy bulbs.
However, I feel that this is less likely to be your explanation. Rodent damage would most likely be obvious in both beds simultaneously. My guess is that your problem arises from environmental pressures and the differences in resistance and tolerance of cultivars planted. One last suggestion I might offer would be that you replant the bed with miscellaneous spring flowering bulbs that are more tolerant of our changeable weather and to soil-borne diseases affecting tulips.