Please goto wp-admin -> wplms -> miscellaneous -> cache duration .
Set 0 there .
refer : http://prntscr.com/hb863v
If above does not helps then Please share your url of the course and admin credentials to check this issue at your end .
PS : mark reply as private while sharing .
Ok spotted the issue .the issue is actually related to your php version .
It is 7.1 .
wplms is not compatible with php 7.1 .
Please contact your webhost and ask them to switch to version 7.0 .