If they have been left unused for a while it is not uncommon for gel pens / gel refills to stop working properly.
Unfortunately, this means that the more pens you have in your rotation / are using at the same time, the more likely you are not using them enough. That’s just what happened to me.
In the case of my Holbein x Rotring multipen the Zebra refill was only two years old. The blue refill is perfectly fine. Being blue meant it got used regularly, but the red refill didn’t get used quite as much, so stopped working. I have replaced it now with a red Lamy refill. The new red colour is grey-ish as is common for ballpoint refills, but it shouldn’t dry out as fast as the vibrant red Zebra JSB refill.
The Gelion refill was older. I actually made a video at the time that shows how to use this refill in a Cara d’Ache 849 …but as the refill was idle for too long it also stopped working.
The final gel-like pen that stopped working recently was Stabilo’s pointVisco. It did survive very long though: I think I got my first pointVisco in 2008, but as I had a set of mixed colours, some of them just weren’t used as much, so stopped working.
There are some common tricks to try to revive gel pens and refills, e.g. putting them in hot water. I tried these trick, but was unsuccessful and have decided to say goodbye to these two refills and the pen.