Problem on meeting planning

For a meeting, it means that resource PM_MLT cannot attend the meeting.
(planning calculation cannot plan work because resource is already busy on another task / or meeting / or has real work registered for this day)

Mettings are always planned before other activities.
But if resource is already busy on another project this may be blocking. In this case, you must find a way to plan together both projects (the project of the meeting and the project using the resource availability on the meeting day)
A work around, in this special case, would then be to directly enter real work for the resource on the meeting, and set left work to zero (to avoid to plan extra work)

All meeting are planned first, even before activities with priority 1 (it is a calculation rule).
If it does not work, check what is planned for the resource on the day, check that the corresponding planning has not "fix planning" checked.