Do a search this has been addressed here. There have been Alt key bugs reported to Adobe. I think the last CC 2018 Update fixed them. One way around the problem for Brush resizing was posted. That was to change the pen bottom button setting from Right Click to Alt+Right Click so the Alt key did not need to be used.
How do you change the button of a surface pen ? this one of the thing this machine is so painful, there are no way to re-assign the buttons.
I do not use my surface pro 3 pen to change brush size I use my Wacom Intuos pro and it pen. or  keys.
Make sure you have the CC 2018 update installed. I think it should solve the Alt keys problems.
Anyone who uses the surface pen on a surface pro with the same issue ? if you have a wacom please consider that I'm speaking about the surface pen only
The Surface Pro Pens Right Click support seems to be a problem. Microsoft Right-Click Support is different then Wacom's Support and even different then Microsoft Surface Touch Pad support With Wacom and even the Surface Pro touch Pad you can just press and hold a button to get a continuous Right-Click. With Microsoft Pen support when you press and hold the Pen button nothing seems to happen till you touch the pen tip to the display. When you touch the display with the pen you get a single right-click. Right-Click and drag is not possible without a continuous Right-Click With the Wacom pen support the continuous Right-click end if touch the display with the pen tip. You drag the pen close to the surface to adjust the brush tip size and hardness. With the Surface Touch Pad you Alt+Right-Click and drag your finger on the touch pad to adjust the Brush size and hardness.
I have never been able to adjust the brush tip with my surface Pro 3 pen in any version of Photoshop. I tried Configurating Windows 10 Pen and Touch with press and hold right click enabled and disabled. I can not adjust the brush tip size and hardness with my surface Pro 3 Pen. I would think the Surface Pro 4 Pen support would be like the Surface pro 3 pen right click support..
i just bought the 2017 version of the surface pro. It was working all fine until the new windows update (just like my surface pro 4). So yes this is a microsoft probleme I guess...
I tried the CC 2018 version as well, still does not work.
This is such a pain !!!! Anyway for now i have configured the key 1 and 2 as the brush size.
I've the same issue but after an hour on Google, finally i've fixed it!!
1) download autohotkey script and install it: https://autohotkey.com/download/
2) download this script: http://www.htdocs.it/sandbox/files/ahk/hover-right-click.ahk
3) download this script: http://www.htdocs.it/sandbox/files/ahk/AHKHID.ahk
4) double click on first script: hover-right-click.ahk (the script will start and you can see the small green AutoHotKey icon in your sistem tray bar
5) open Photoshop, take your pen near the display, press ALT key + Surface Pen right click BUT not touch the screen. Simply moving your hand left/right to resize the brush
hope you solved your issue too
sorry for my bad english :-)
Thank you so much !!!! this saved my life !!!!! Just a question , what is the second script for ?
happy to help!
that script has provided by Justice from Tablet Pro but I don't know how it works. inside the first script you can find an "include" function to the second one, so you can't use the first script standalone
I found it in this forum: https://autohotkey.com/boards/viewtopic.php?t=30422
I've tested it in my surface pro 3 and it works great!
months later and this is still not solved by adobe/microsoft....the autokey still makes the job