constrained type won't unify

Filter.purs

type ProjectColumnFilter =
  { prop :: forall label a r'. IsSymbol label => Show a => Cons label a r' Types.ProjectRow => SProxy label
  , propFilter :: PropertyFilter
  }

filterProjects :: Pattern -> Array ProjectColumnFilter -> Array Types.Project -> Array Types.Project
filterProjects pattern columnFilters projects =
  Array.filter (\proj -> matchesPattern proj && matchesFilters proj) projects
  where
    matches pat val = contains pat (toLower val)
    matchesPattern proj = matches pattern (show proj.code) || matches pattern proj.name
    matchesFilters proj = and $ (\{prop, propFilter} ->
      let propValue = show $ Record.get prop proj
      in case propFilter of
            StringPropertyFilter str ->
              matches (Pattern str) propValue
            RangePropertyFilter start end ->
              readFloat propValue >= start && readFloat propValue <= end
            SelectionPropertyFilter str ->
              propValue == str
      ) <$> columnFilters
      
 
 {-
 error is on the last line, on `columnFilters`:
 
 Could not match constrained type

    IsSymbol label3 => Show a4 => Cons label3 a4 r'5
                                    ( id :: ProjectId, ... )
                                   => SProxy label3

  with type

    SProxy t1


while trying to match type IsSymbol label3 => Show a4 => Cons label3 a4 r'5
                                                           ( id :: ProjectId, ... )
                                                          => SProxy label3
  with type SProxy t1
while checking that expression columnFilters
  has type t0
             { propFilter :: PropertyFilter
             , prop :: SProxy t1
             | t2
             }
in value declaration filterProjects

where r'5 is a rigid type variable
      a4 is a rigid type variable
      label3 is a rigid type variable
      t0 is an unknown type
      t2 is an unknown type
      t1 is an unknown type
-}