Develop settings partially lost

I am experiencing a new problem on LRC that I hadnt encountered in the past. My main working catalogue which contains around 90.000 raw images, has lost the develop settings for images older than aprox. 1 year. Newer images with develop settings are marked with the +/- symbol and when opened in the develop section, show the transformed/developed image. The older images, which have been developed/transformed, also show the +/- symbol, but when opened in the develop section show the "untouched" raw file, as if no settings had been changed. So LRC seems to "remember" that these images have been worked (thus the +/- symbol in the library overview), but apparently cant find the settings for these older files, although its all one catalogue and it does find the seetings for newer files. The problem suddenly appeared, its a bit difficult to explain, but maybe somebody has encountered smthg similar.