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 ;)