I hope this information will help others.
My Ischia starter has always been stored at 40 F in the fridge and it's been performing amazingly. At this temperature, it's not frozen but is very thick. My procedure was very simple; I always have 650g stored and for preparation I just add 150g flour and 150g water. When it's full active, I take what I need and then store a new fresh 650g. This will have some ~250g discarded. This procedure has been keeping it healthy for the past 4 months with weekly use. Notice that I don't feed again before storing.
In the first couple of uses, it was performing the same but it seems like the temperature change needed some time to take effect. Yesterday when I took it out of the fridge to make the dough, it had some black spots and it smelled differently. The texture was also different; it lost its thickness that I'm used to and now it's more liquid. After I fed it for preparation, it took half an hour longer to reach it's full activation point.
The dough was room temperature fermented for 17 hours at 75 F and then balled and proofed for 3 1/2 hours before bake time. I noticed that the dough also showed those black spots and it had lost the elasticity that I'm used to. During the proofing, the dough balls did not expand as much as they used to.
Handling the dough was rather simple but there were no bubbles this time. Also during baking, there was a lack of oven-spring. The pizzas were ok but the crust was not as fluffy. It was more on the dense side.
What I believe is that the Ischia was a little active at the 50 F storage temp and this gradually decreased the active population of the starter resulting is slower preparation time and less dough ball proofing expansion. It had also affected the elasticity of the dough somehow.
The Ischia would have probably needed to be fed again after preparation when stored at this new temperature as to preserve the active population. I will start doing this from now on and keep using the 50 F storage temp for a while and see if this will change things. Otherwise I will go back to my previous storage temperature of 40 F as it was easier and maintained a healthier Ischia.