All Market Watch Symbols - Some symbols doesn't start simulation from the first ticks



I have imported custom symbols ticks from CSV. I have generated bars with an EA script.

When I launch a simple script with strategy tester for a single symbol I got the excepted results.

But when I try to launch the same script on All Market Watch symbols, some of the symbols (but not all) trigger the first OnTick event at the date of the first tick of the previous symbol (whereas the symbol has ticks before the previous one)

I use the option : entire history and Every ticks base on real ticks.

Is there a way to launch All symols test on the entire history even if the history of each symbols start at different time (first tick) ? Or should I add empty ticks to set up the history of all symbols starting at the same date ?

Thank you for your help.