In targets 0.14.0:

If you continue in the debugger, the target will ignore any debug(your_function) calls and return the quoted expression in target$command$expr rather than the result of evaluating target$command$expr. The code excerpt in R/class_builder.R needs to be this:

target$command$expr <- c(
  expression(targets::tar_debug_instructions()),
  expression(browser()),
  target$command$expr
)