I am not familiar with the menu layout of 5.50.4 ...suggest you navigate through various buttons to see if SYMBOLS is available.... alternatively check the manual...otherwise wait for some expert to resolve your issue...!!!
i have similar problem, suddenly i found the many symbols missing eod ,( in database all symbols are available ) only A series of stocks like ACC ALBK datas are showing in amibroker, rest all it is blank ,,, pse guide me to restore that
thank you