I suspect a large fraction of the people who are having this problem have failing batteries. It would be useful to know how old the machines are and how much of their life has been spent at full charge connected to external power supplies.
Since Surface Pro 4 is released in 2015 and Pro 5 2017, I assume most devices are more or less 3 years old.
My Surface Pro 4's battery is still relatively healthy. It has more than 90% juice according to battery health report. When fully charged, I can play streaming videos on medium brightness continuously for at least 4 hours.
The only problem is that it keeps burning 5 - 10% battery per day when the machine is fully shutdown (no connected / modern standby, no waking the machine for scheduled tasks)
It is also not a new problem to me. This problem started appearing when my machine is roughly 1 year old and I have strugged with this problem for more than one year.