Reporting again here as we still have this error

openxlsx::read.xlsx("C:/Users/jmbar/Downloads/bad.xlsx", detectDates = TRUE)
#> Error in read_workbook(cols_in = cell_cols, rows_in = cell_rows, v = v, : basic_string::substr: __pos (which is 8) > this->size() (which is 7)

^{Created on 2021-11-06 by the reprex package (v2.0.1)}

Original

I can confirm the issue is still there. See the file attached, opening it with detectDates=TRUE raises an error:

Error reading date:
44489.4
row: 1
col: 1
Error in read_workbook(cols_in = cell_cols, rows_in = cell_rows, v = v,  : 
  basic_string::substr: __pos (which is 8) > this->size() (which is 7)

bad.xlsx

Originally posted by @aushev in awalker89/openxlsx#249 (comment)