Steps to reproduce:
Create 30 forwarding addresses.
Create 30 filters, one for each address.
Delete non-essential information in XML file, keep only tags with expressions and actions.
Delete all filters in Gmail UI.
Import them with Gmail UI.
Repeat #5,#6 multiple times.
At some point Gmail will not import all 30 filters.
I believe you will be able to reproduce with 10 addresses and multiple re-imports.
Does anybody know what is that Google internal Gmail threshold that I hit and what are specific parameters of such threshold? And also why does Google put such limit at all? Is this a bug? How to make Google fix that bug?