Too many different related threads, sorry.
This is rather a technical issue. IB decided that the fund you own is not traded enough and is not liquid enough under the ticket (exchange/currency) you have bought it. You can of course sell your position, convert the currency and buy it as the most traded ticker version. I don’t know if it is possible to ask IB to convert your position from one ticker to another, as it is a technical issue after all.
Against all of them. As long as your net equity (stocks value minus debt) is higher than the margin requirements (typically 50% for regT margin), you are fine.
On the other hand, if your margin requirements are not fulfilled, IB seems to sell positions rather randomly.
And 20% is not small, I would limit to 10% if you don’t have experience and not sure how it works.