Variable getting Reset

Your screenshot is deficient. I cannot see the rest of the chart. Which means I cannot see if there is any right-expansion area. But more importantly, I cannot see the ticker symbol or the time frame used. Which means I cannot replicate the chart on my system.

If one plots correctly and the other does not, why not just use the logic from the one that plots correctly for all of them? You say you want to plot chart bubbles in the mid point of a plot. Your comments indicate you have one that does that, and that you know which one that is :

AddChartBubble( barNumber() == TotBars / 2 or barNumber() == ((TotBars / 2) + .5), 0, Concat(barnumber(), totBars) , Color.YELLOW, yes);

The part of that code that determines the horizontal position of the chart bubble is this:

barNumber() == TotBars / 2 or barNumber() == ((TotBars / 2) + .5)

So use that for all of them. Problem solved. Although I am a bit concerned that you have an OR in that statement. Unless you are trying to plot the chart bubble along two different points of the horizontal axis, that OR should not be there. Which means the section on either side of the OR is likely producing the same exact result.

Attached screenshot is your code, adjusted to troubleshoot the issue. To troubleshoot the issue and demonstrate the answer to your question I merely turned off all plots and converted your lastBar variable into a plot.

declare lower;
def Line1=1;
def Line = 0;
plot lastBar = if IsNaN(close())then double.Nan else barNumber() ; #(last bar was at 61)
def TotBars = HighestAll(BarNumber()); #(including 10 bar expansion, total bars=71)
#AddLabel( yes, Concat(lastBar, TotBars), Color.RED ); # shows correctly 61 and 71
#AddChartBubble( barNumber() ==lastBar/ 2 or barNumber() == ((lastBar / 2) + .5), 1, concat(barnumber(), lastBar ) , Color.YELLOW, yes); #prints at bar#1 and shows LastBar=1
#AddChartBubble( barNumber() == TotBars / 2 or barNumber() == ((TotBars / 2) + .5), 0, Concat(barnumber(), totBars) , Color.YELLOW, yes); #prints correctly at bar 36 shows totBars=71

In the screenshot, you can see the value of the lastBar variable is incremental. It increments by one for each bar on the chart. Right expansion area is excluded. BarNumber() begins at the left and increments for each bar until the last bar on the chart.

Your statement for this variable: def lastBar = if IsNaN(close())then double.Nan else barNumber();

Is exactly the same as this: def lastBar = barNumber();

The value of the level One chart bubble will change depending on where you place it on the horizontal axis.

You are likely to have more questions but what I want you to take from this is the method I used to troubleshoot the issue. Whenever you get unexpected results, break everything down into the smallest functional piece and plot the values on the chart. Until you can visualize all the individual pieces you don’t have any hope of understanding what is going on. Software developers use a debug log. We must use plots on a chart.

What happens when you plot: barNumber() ==lastBar/ 2

What happens when you plot: barNumber() == ((lastBar / 2) + .5)

Question everything until your assumptions are replaced with empirical knowledge. That’s when everything becomes clear.