Tablet pencil freezes during the Zoom class

Hello!

I'm a lecturer. I usually share my screen and write/draw the equation and figure by using the Wacom tablet.

This works well if there is only me in the zoom meeting.

However, if students (13 people) join the meeting, the tablet starts to become extremely slow and it's almost impossible to write anything (If I write the letter ridiculously slowly, then maybe it works).

Since Wacom tablet works well if I am alone in the zoom meeting, I don't think this is the problem with the tablet.

I used LAN cable (not wifi), thus my internet speed is fast enough.

I ask all students to turn off their video.

I use the Wacom tablet (WACOM INTUOS CTL-4100).

I really want to solve this problem. 

Any comments or suggestions would be welcome.

I appreciate your help in advance.