Silverfish & Endermite spawners no longer functioning

Silverfish and endermites no longer spawn from mob spawners, and the spawner delay instead becomes stuck at 0. This seems to happen regardless of light level, player proximity, available spawn space, biome, or nearby terrain. Silverfish and endermites appear to be the only mobs affected, and the mob spawner functions normally if it is set to spawn any other mob. This was not the case prior to 1.14.3.