[OPPID SS10] Failed to show existing available connectors

Hello All,

There is a project which is OK for long time, but it cannot show available connectors suddenly, When it happened on the first time, I noticed that there were empty value in the database table PID_TOFR.MATCH_KEY, I changed the empty value to NULL, the available connectors displays. But several hours later the problem happened again. There is no empty value in the database table PID_TOFR.MATCH_KEY now, I also check ed other fields, all the field type are string, no unusual text. Anyone know what's the problem, or what's the background SQL script when we search in OPPID? Thanks.