Why is Microsoft Solver Foundation not returning a solution?

Question

I'm trying to solve my linear program with Microsoft Solver Foundation, but it doesn't return a solution. It doesn't give a clear message to what is wrong, so I'm not sure what is going on. I have checked the constraints and I believe they are coded correctly, but maybe the LP model is wrong on itself? I would be glad if you can take a look at it and see what's wrong :)

===Solver Foundation Service Report===
Date: 15/10/2021 16:00:21
Version: Microsoft Solver Foundation 3.0.2.10889 Express Edition
Model Name: DefaultModel
Capabilities Applied: MILP
Solve Time (ms): 51
Total Time (ms): 103
Solve Completion Status: Unknown
Solver Selected: Microsoft.SolverFoundation.Solvers.SimplexSolver
Directives:
Simplex(TimeLimit = -1, MaximumGoalCount = -1, Arithmetic = Default, Pricing = Default, IterationLimit = -1, Algorithm = Default, Basis = Default, GetSensitivity = False)
Algorithm: Primal
Arithmetic: Exact
Variables: 133 -> 133 + 40
Rows: 40 -> 40
Nonzeros: 522
Eliminated Slack Variables: 0
Basis: Slack
Pivot Count: 0
Phase 1 Pivots: 0 + 0
Phase 2 Pivots: 0 + 0
Factorings: 0 + 0
Degenerate Pivots: 0 (0,00 %)
Branches: 0

I'm making this for a practical assignment, so I prefer not to share my code. For information about the assignment: it's a machine assignment problem, where you have to plan two appointments for all patients. There are global parameters:

• p1: the duration of the first appointment
• p2: the duration of the second appointment
• g: the gap between the first and second appointment

Each patient needs two appointments t1 and t2 that need to be planned. Each patient also has personal parameters:

• interval I1=[r1, d1], the time interval in which the first appointment can be planned
• x: (personal) extra gap between the first and second appointment
• length l, the length of the second time interval. I2=[t1 + p1 + g + x, t1 + p1 + g + x + l - 1]