Tumblr’s iOS app is missing from Apple’s App Store. Tumblr says that it is “working to resolve an issue with the iOS app,” but it’s not clear if the app is missing from the store because it was removed by Apple, or by Tumblr itself.

Earlier this week, users reported that there were issues with searching in the iOS app while Safe Mode was off. According to PiunikaWeb, Users who deleted the app in an attempt to reinstall it discovered that it was now missing from the App Store, although some users reported that they could re-download the app by going to their purchases page. As of this afternoon, Tumblr noted that it was “still working on the issue with the iOS app.”

It’s not immediately clear why the app isn’t available, although there was some speculation that there might have been due to a certain type of inappropriate content. We’ve reached out to Apple and Tumblr for comment, and will update this article if we hear back.

Apple has removed apps from the store in the past. Earlier this year, it booted Telegram after it became clear that the messaging app was being used to distribute child pornography. Apple’s iOS guidelines make it clear that any apps available on the store must have some sort of content filter to screen out such material, and Tumblr is famously permissive of NSFW and adult-oriented content. This has caused headaches for the company before — in 2016, the Indonesian government blocked the site for a short while over adult content, although it reversed its ban a day later.