rangeToArray tries to read every possible cell leading to OOM about phpspreadsheet HOT 1 OPEN

Not a bug, and nothing to do with the Reader. The Reader reads the spreadsheet file, and the values returned for a worksheet by getHighestColumn() and getHighestRow() are calculated based on values stored in the file, and cells that are referenced in the content of the file (perhaps by style information or range settings). getHighestDataRow() and getHighestDataColumn() are calculated at the point when they are called, and based purely on cells that contain data.
The toArray() methods use the getHighestColumn() and getHighestRow() values, changing it would be a BC break; but rangeToArray() can always be used with the getHighestDataRow() and getHighestDataColumn() values... that's why we provide the method.
We don't recommend the use of toArray() or rangeToArray, because creating a large PHP array will always demand a lot of memory. Instead, we'd recommend using the row and column iterators.

from phpspreadsheet.