How to fix shift/reduce conflict using GLR

Lezer
1 
@top Program { line* }

line {
  DerivativeLine  | AssignmentLine | Newline
}

DerivativeLine {
  DPrefix NumeratorVar Slash DPrefix DenominatorVar Equals Expression
}

AssignmentLine {
  AssignmentVar Equals Expression
}

DPrefix        { lower_d ~ambiguous }
NumeratorVar   { Name            }
DenominatorVar { Name            }
AssignmentVar  { Name  ~ambiguous  }
Equals         { "=" }
Slash          { "/" }
Newline        { newline1 | newline2 }

Name {
  (lower_d | lower_not_d | upper | "_") 
  (lower_d | lower_not_d | upper | "_" | digit)* ~ambiguous
}

// consumes characters, but not newlines, meaning DerivativeLine and AssignmentLine always stop at newline
@external tokens expressionTokenizer from "./tokens.js" {
  Expression
}

@tokens {
  lower_d           { "d" }
  lower_not_d       { $[a-c] | $[e-z] }
  upper             { $[A-Z] }
  digit             { $[0-9] }
  space             { " " }
  newline1          { "\n" }
  newline2          { "\r\n" }
}

@skip { space }

shift/reduce conflict between
  (lower_d | lower_not_d | upper | "_" | digit)+ -> · lower_d
and
  DPrefix -> lower_d
With input:
  lower_d · lower_d …
The reduction of DPrefix is allowed before lower_d because of this rule:
  DerivativeLine -> DPrefix · NumeratorVar Slash DPrefix DenominatorVar Equals Expression
Shared origin: line+ -> · line
  via line -> · AssignmentLine
    via AssignmentLine -> · AssignmentVar Equals Expression
      via AssignmentVar -> · Name
        via Name -> lower_d · (lower_d | lower_not_d | upper | "_" | digit)+
          (lower_d | lower_not_d | upper | "_" | digit)+ -> · lower_d
  via line -> · DerivativeLine
    via DerivativeLine -> · DPrefix NumeratorVar Slash DPrefix DenominatorVar Equals Expression
      DPrefix -> lower_d ·

Hi, my language is basically (line \n)* and there are 2 possible lines:

dx/dt = … (example of DerivativeLine)

name = … (example of AssignmentLine)

But the DPrefix could also be the first character of an AssignmentVar (e.g. ddd = …). The way to choose is whether a Slash appears before encountering Equals (if it does: DerivativeLine, if it does not: AssignmentLine). But I cannot seem to fix it using GLR and I don’t understand why. And some of the features like precedence, dynamic precedence, specialize/extend, I don’t really understand either, if they are even the solution here. I have tried placing ‘~ambiguous’ in many different ways, but the error remains.