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Yes, I had this problem too. I know this is about 3 years after the original post but for anyone else having this problem after this, it might help you.
This is for the Zeppelin. You might notice there is only the channel and the clip at the tips to hold the plastic grille cover on. But once you have slid the cover onto the channel and toward the last 1/3 of the travel, it flares out. That’s because there is a narrowing of the channel as I have shown in the picture. You must ensure the cover actually engages into the narrowing part and not miss it or it will be on the outside which is what make sit flare out. Keep it well aligned. It will then be as difficult to push in the last cm as it was to remove it.