Q: My 2 Range chart fills within an hour or two (on a fast day in 15 minutes) and the bars re-size and the marking and indicators are gone due to resizing.
A: On the chart property form are 2 parameters for Save/Resize and Maximum Bars.
Here is how these 2 values work together. When a chart is opened it loads with the Save/Resize quantity. Then the chart grows until Maximum is reached, at which point the chart trims back to the Save/Resize quantity. So to reduce the frequency of resizing (which also causes a recalculation) make the 2 numbers further apart. In the example shown, this 5-min chart will collect 60 bars before resizing. This would be 3 hours of collection. Your 2 Range charts is building bars much more quickly, so a separation of several thousand might be beneficial so you resize infrequently. Your discussion of 300 and 10,000 sounds like the right idea, but I have not seen your entries to verify if 300 is your Save/Resize value and 10000 is your Maximum Bars value. And when it resizes to 300 the draw tools are removed that have anchors in the bars that are clipped from the file. Only the last 300 bars are retained.
What you are seeing and calling resize might be something else, such as how often the chart is shifting leftward. To reduce the constant repaint of moving the chart just 1 bar leftward, we do have a parameter used for tick based charts of moving the chart several bars leftward so there is more margin in which to build several bars before another shift left is performed.
On the Setup | Charts form see the value pointed to by the arrow. This is the number of bars to shift leftward. So the jump left is every 10th bar, and the margin will have room to build 10 bars before the left shift again. Perhaps it is this operation you are calling resize. Try 20 and see if that is helpful to what you see.