Question: Solve() with assumptions

I have a linear system of 3 equations in 3 variables and have no issues with solving it using solve().

I am having issues with solving it by imposing assumptions on my parameters. The infolevel[solve] now outputs "Entering solver with 6 equations in 3 variables", so I am likely making mistakes in the syntax solve(Eqs, Vars, UseAssumptions) assuming ... first of all, do I even need to do this given the assume statements that I set up on top of my script? How do I make sure that all the assumptions are preserved throughout all the calculations in my worksheet?

Moreover, I don't know why I get SolutionsLost: setting solutions lost flag.

My script:

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