I also had this problem using Android App and Vectornator (Being too cheap to pay for adobe illustrator and all the cloud subscription stuff that goes with it). Haven't fully solved the problem yet, but the problem lies with Vectornator's JSON code with opacity. If you remove all opacity it will work better. Another thing is that it really appears to save a bitmap and wrap it in SVG code instead of being a clean SVG code, and a lot of online resources do that. If you open the code of the image you will see in the javascript that the code isn't quite right, which is probably why it is free. Moreover, Android has not gone out of its way to make itself compatible with a program like Vectornator, but they do go out of their way to "play nice" with adobe programming. I have come up with these solutions:
Pay for and download a program like Affinity Designer for $9.99 on Ipad (1 time fee) which has a cleaner formatting capability and import it in there then turn to SVG (and fix the issues in the design as they pop up.
Use Vectornator only for art, and not for programming, and then buckle down and use Adobe Illustrator because let's face it, they have a lot of money behind them to make sure that their products "play nice with others" (Meaning they actually pay Android to provide programming to support their code).
Import a ton of code from Maven Libraries for SVG support and essentially build an in program svg to png converter that replicates what Android App does when it imports a vector, but is under your control. If you do this you will upload all your svg files directly to this mini program instead of using the Android App's Import Image and Vector directory under File New.
I was trying everything but using Adobe Illustrator, but it is a huge pain and a lot of headache. Adobe Illustrator still has minor issues, but not the huge glaring problems of Vectornator.