This problem, which I have only noticed on plastic-backed plates, is often easily cured. After the normal procedure of spraying and sponge drying the plate, try blowing the moisture off with a can of compressed air until the floor appears to be clear of water droplets. Put the plate in the dryer but check on it every couple of minutes or so. Amazingly, this can often solve the problem. Note again though that a complex imaging configuration may not allow for this quick fix.
Custom plate processing: Sliding of hairline rule and embellishments
Dependent upon the configuration of the imaging (usually raylike or circular patterns), sometimes distortion of hairline rule and similar extremely thin font or image embellishments can be corrected with increased exposure and less washout. This is the normal procedure. If, however, even after correction, the washout reveals the imaging to be stable but after oven drying it is distorted, the drying out process is the culprit. Imaging with minimal relief structure can actually slide out of position because of the contracting nature of the heat and the slippery wet pre-exposed photopolymer floor of the plate. Note that manufacturers back expose sheet photopolymer plate material before attaching to the backing, thus the floor is insoluble and is a plane of demarcation.