If the electrode shows unstable potential, the liquid junction is probably clogged, if the electrode is new, it is due to crystallization.
Crystallization is difficult to avoid as the small crystals have tendency to form a big single crystal. It becomes critical when the big single crystal blocs the liquid junction (porous pin) and generates unstable measurements. This can be avoided by adding from time to time deionised water in the reference part of the electrode and holding the electrode upside down in order to free the small crystals. Crystals must however always be present to guaranty the inner solution is saturated. It is however sometimes necessary to flush the inner compartment of the electrode with filling solution before the small crystals from a conglomerate.
If the liquid junction is blocked with big single crystal, immerse the electrode in hot water and rinse the electrode with deionised water inside.
As soon as the electrode is free inside, it means there is no crystal conglomerates inside any more, remove the deionised water and refill the electrode immediately with filling solution. Prolonged contact of the inner reference element with deionised water must be avoided as it will dissolve the reference element and slowly destroy it.
Then add crystals, there should not be too much crystals inside the electrode because it increases the risk of clogging the liquid junction again. Ideally there should be around 3 mm height crystals that are free from each other. Free crystals do separate when the electrode is turned upside down.