I tested the behaviour many times by enabling and disabling the USB-Tethering from Android phone.
I found out, than if there are more than 7 pictures on the phone, the MTP connection is VERY slow => bug
If I delete some photos, less than 7 pictures, MTP then works, but if I make some new photos MTP it is very slow again => bug
I can confirm, the bug exists in Ubuntu 18.10
I tested the behaviour many times by enabling and disabling the USB-Tethering from Android phone.
I found out, than if there are more than 7 pictures on the phone, the MTP connection is VERY slow => bug
If I delete some photos, less than 7 pictures, MTP then works, but if I make some new photos MTP it is very slow again => bug