I am working with panel data and xtreg with fixed effects.
3 of my variables result in Omitted after running the regression. I checked the possible following reasons but non of them are met:
1. collinearity problem
2. having "." values in the variable
3. the problem of invariant variables

Would you please guide me what else I could do?
One of the problematic variables is dummy (with 171 values of 1 and 434 values of 0) and the remaining two are continues while have more than half of the values equal to zero