You are supposed to rinse out the nib and feed periodically. There are several ways to do it, but at least rinse the nib and feed until the water that drips out of the nib isn’t obviously colored, soak it in some water for an hour or so to get even more gunk out, then put the nib point down on a paper towel or something to suck even more old ink out, and then give it some time to dry.

You don’t need to do as much if you’re just refilling it with the same color, but since you’re running into trouble might as well rinse it out fairly well.

That just might fix the problem if it’s built-up dried ink clogging up the pen.

FYI, Never had any issue with Lamy and their (official) converters (the only difference being that they carry less ink than a cartridge), no matter the ink brand I have been using. And I have been using Lamy since the late 90s.

• As suggested, you may want to rinse your fountain pen (and let it dry for a few days). You may also learn to disassemble the fountain pen entirely (which for a Lamy Safari means removing the nib and the feed) to do a deep cleaning (you will find guides on YT). When not using a fountain pen for a long time, ink can dry in it and should be cleaned (with standard ink, barely warm water should be more than fine)
• Waterman, like Pelikan, is a great (and cheap) ink, I’ve been using it since I was a kid (back in the 70s ;) but you may want to check what exact type of ink you’re using. Make sure it is ink for fountain pens and not India or acrylics which would ruin any fountain pen.
• Another possibility: check you’re using a genuine Lamy converter. There are cheap knock-offs. And just in case: don’t try to use a Lamy converter on any other brand of fountain pen.
• Last suggestion: contact Lamy support. They’re not the fastest but they’re good. I had them help me with a 2009 model a few months ago, without any issue. I place them right next to Twsbi as far as customer support goes, and Twsbi is real excellent ;)

@Shalaska
Ive just pulled out my one Lamy converter.
The converter in the photo does not look like a propriety Lamy converter, It looks like an International Standard converter. In which case that would account for leakage and poor performance.
Lamy. most of the Japanese, Shaeffer and a few other manufacturers use propriety cartridges and converters that are not interchangeable with other brands.
Some Chinese pen models claim to use Standard International cartridges but they are sufficiently out of dimension that only their own products will work.