The bug needs forwarding to the Tcl/Tk community. This is the script written in Tcl (run with tclsh8.6 script.tcl for Tcl 8.6 and tclsh8.5 script.tcl for 8.5):

package require Tk

scrollbar .vbar -width 10
text .edit

pack .vbar -side right -fill y
pack .edit -side left -fill both -expand 1

.vbar configure -command {.edit yview}
.edit configure -yscrollcommand {.vbar set}

bind .vbar {<Button-1> } {
	set cx %x
	set cy %y
	set dz [.vbar identify $cx $cy]
	puts "You clicked at ($cx,$cy) on $dz.\n"
}

for {set i 1} {$i <= 256} {incr i} {
	.edit insert "$i.0" "This is the line number $i.\n"
}

I will post two videos made on my MacBook, showing an expected behavior with Tk 8.5 and the scroll problems with Tk 8.6 on macOS.