How do I address unbalanced panel in synthetic control?

I am trying to use the synthetic control method to test the effect of a university closure on one party's vote share in the district where the university closed. I can get it to work just fine with the one election before the closure and the one time period after and I now have covariates and election results that stretch back about four elections. However, I am concerned that this creates a new issue. Specifically, the boundaries of the electoral districts changed in the pre-treatment period, leading to different district names in the pre-treatment period. I fear that this is leading to an unbalanced panel. Fundamentally, is the synthetic control method compatible with changing boundaries of and compositions of units in the pre-treatment period? If it is, what is the fix for this problem? Error in dataprep(foo = out, predictors = c("francophones_pct", "mining_pct", : Your panel, as described by unit.variable and time.variable, is unbalanced. Balance it and run again. A sample of my dataset is below along with reproducible code which produces the error: out