Custom Volume Profile - Fix

I'd like to improve this MT5 Indicator,

it's a custom Volume Profile inside a rectangle, which the user can draw on the chart:

1) Error Fix:  Sometimes I get an error message "array out of range":

The rectangle then is empty, and even when I drag it, there appears no volume histogram inside. It seems the indicator can't find volume data or so, I don't know. But often when I switch to another time period and back, the error is gone and the rectangle appears again.

I'd really like to have this explained and fixed.

2) Sometimes I don't know if the indicator still loads. Maybe it can be improved somehow so that it loads faster.

I need the source code, too. It should be included in the price.

Maybe I'd buy another Volume Profile Indicator instead of these changes:  If it's simple, fast, without tons of preferences, and accurate (M1 data). I'd prefer one which I could draw whith two vertical lines instead of a rectangle.