What are potential problems that collinearity occurs and coefficients are omitted? What should I do to deal with this problem? Should I change the way to run panel regression? or what is the potential wrong with the previous?

- xtreg Insales Incapital Inlabor Inaterials, fe note: Incapital omitted because of collinearity. note: Inlabor omitted because of collinearity. note: Inmaterials omitted because of collinearity. cd D: Istata is append using "Montenegro--panel data-.dta" "Montenegro_2009_2013_2019.dta" "Egypt_2004_2007_2008_2013_2016_2020.dta" "Czech Republic--panel data-dta" "Czech Republc_2009_2013_2019.dta", force rename year year rename panelid panelid rename b2c soe rename b2b foreign rename j2 reg_time rename j6a gov_contract rename d2 sales rename d3c sales_exp rename 11 employees renane n6a capital rename n2a materials gen exp_dum= (sales_exp>e) gen foreign_dum= (foreign>e) gen soe_dum=(soe>0) sunmarize year panelid soe foreign reg_time gov_contract sales sales exp employees capital materials bysort panelid year: gen count = N duplicates report panelid year bysort panelid year: drop if N>1 xtset panelid year gen Insales=ln(sales) gen Incapital=ln(capital) gen inlabor-1n(employees) gen Inmaterials=1n(materials) xtset panelid xtreg Insales Incapital Inlabor Inmaterials, fe gen Inexp_dum= In(exp_dum) gen lna=ln(a3) gen lna1a=ln(a1a) xtreg Insales Incapital Inlabor Inaterials Inexp_dum Ina3 Inala,fd