Since we've got some inquiries about the solution. Here it is.

We have filed a bug to AppsFlyer* and they have fixed the issue.
So the solution is to update the SDK version to the latest. They fixed the issue in 6.10.1 https://support.appsflyer.com/hc/en-us/articles/115001256006-AppsFlyer-Android-SDK-release-notes

*It was an AppsFlyer bug