After some sort of teleports, gamemode changing and inventory clearing, then whenever I held down the screen with tools of any tier in the hand and catch the PlayerActionPacket, the inventory wiped out. Still can set the item on the inventory though, but after that none of the tools can he held down to be used. Re-login solved the problem. With the first chain of teleport and gamemode changing everything works fine though. No pattern has been found. I maybe have some clues: the items have custom names, I'm making minigame server, it's with plugins. Anything I can debug with?
If you're on Windows 10 edition, than you have to go to settings and change the UI from Classic to Pocket. The classic UI is buggy, but that's Mojang's fault.
Going to retry with Pocket UI to see if it happens or not. I was reported that some clients have this problem with their phone too, though I would reply in future.
It is possible to use the Classic UI in pocket edition as well. I once tried it myself when I was trying out a device to connect a computer mouse to my android tablet. I would ask them what their settings are.