Based on the title of your request, you doubt the stability of Ag/AgCl el-de (RE), but what you measure is, I presume, OCP between RE and your working electrodes (WE; W and Mo). In this case, OCP reflects redox processes at both electrodes. Also what is the time-scale of measurements? You can, at least, check stability of the RE by running some simple voltammetric measurements (like CVs for ferri-/ferrocyanide couple) on Pt or Au el-des. E1/2 should not change, but make sure that solutions are always fresh and the WE is cleaned prior to each measurement.

@John H.T. Luong I currently mainly focus on  the  basic research. Some electrochemical techiniques are employed to study the electrochemical behavior of Lanthnides and Actinides ions in LiCl-KCl eutectic. This is the electrochemical measurements that I mentioned.

Recently, in my experiment, the peak-to peak separation will be close to the value:60mV from CV results. moreover, the  deviation in each measurement  is not very stable. therefore,I think the stabilty of the reference electrode is important, but I don't know how to make a stable reference electrode for accurate results. It really makes me very distressed.

To my knowledge, the corresponding temperature of the theoretical value:56mV obtained is 25 degree.  I contact with electrochemical soon, also please the teacher more guidance. 

Thank you for your reply.

@Anatolii Cuharuc Indeed, for the stability of the reference electrode, I only judge by the CV results in the experiments. Before my experiment, check stability of the RE by running some simple voltammetric measurements (like CVs for ferri-/ferrocyanide couple) on Pt or Au el-des, is this your meaning? Sorry,I don't catch your meaning.

Thank you for your kind reply and suggestion.

Yes, I change another reference electrode in experiment. Here, it is not clear to me what reasons can result in the potential disparity. Because of the frequent changes, each measurement result undoubtedly will inconsistent.. Therefore, I think the stable reference electrode is very important, especially, electrolysis experiments

most likely you have a troubled commercial electrode and trying another one can be the first thing to do. but it is good to be able to check your RE when in doubts. Yes, that is what i meant: running  CVs of simple well-known redox couples. They should come out standard. But your primary concern is the position of CV on the potential scale.