What version of Reader are you using? Please check if there are any available updates for the version installed on your machine.
Also, What OS are you using?
Does this happens with a specific pdf? If yes, Please attach a link to the file.
Version installed in the machine is Version 15.3, build 131442 on Android OS version 5.0. No updates available the reader.
Link is as set out below - not sure if you are able to access it.