Polestar2021,
My first comment is that a plan that has that many resources assigned to a single task is either, a) to detailed with resources, or b) not detailed enough with respect to tasks.
So what does that mean? Let's say of the 60 available resources instead of 60 individual unique skills you actually have 20 of one compatible skill, 20 of another compatible skill, 10 of another skill and 10 individual resources with one-of-a-kind unique skills. Of those resources with compatible skills you may not care which individuals work on the task, they all have equivalent ability. For those resources you should consider creating group resources (e.g. Elect Engr, Mech Engr, etc.) where the Max Units for each group equals the number of individual members of the group. So, if the Elect Engr group has 10 people, the Max Unit value for the group is 100% x 10 or 1000%. This assumes a single Base Calendar for the group. Using group resources can greatly simplify resource utilization by not getting bogged down in unnecessary detail.
For part b) your plan may not be broken down in easily manageable tasks (i.e. it is structured at too high a level). Depending on the total span of the plan a good starting point is tasking in 2 to 4 week elements. That is, a single task should not span more than 2 weeks to a month. Although this may seem to expand the total scope of a plan, that expansion can be controlled by expanding only the near term effort (e.g. 6 months) while keeping future tasks as "planning packages" to be expanded as the plan progresses.
So yes, the very likely could be something wrong with your setup.
John