This is a follow up of my Canvas flicker I told some days ago. The Set EraseBackground trick works fine excepted in some windows and I do not know why. For this, Ive made a simple test, I cleared cache, trashed and erase it all previous applications, build the application after making needed changes, quit Xojo, power off the computer, take a breakfast (too fast), Powered on, check the Xojo cache and Trash are still empty, launch Xojo, the project generate the windows application, check my Memory Stick against any older version, copy the new application, move the MemoryStick in the WIndows 10 1803 machine and run
to still get the flicker in the same windows and no flicker in other windows 
Then, only for a test, I commented in a "bad window"s Canvas Paint event the code to paint a Picture.
I run the application (in the IDE), and without surprise, the image does not appears.
Quit, back to that window, canvas, I uncommented the code in the Paint Event, run and the image does not appears.
I saved the modified project, run: still no image.
I closed the project, open it back, run and still no image !
The image is still here since I display it elsewhere in the application.
Nota: I cleared all given license in my account / xojo web site. I was not connected to the internet. I cleared the Xojo cache folder. Beside sending that computer thru the room window, I do not know what to do anymore and these mysteries comes now and then, followed by a period of safety (everything is OK), then come back.
Last tests: I open that project with Xojo 2017r1.1 and run it; the image is not displayed in the Canvas !
I saved the project to xml and found the old Activate event with code: I cleared it an hour ago. Also, I loaded that xml in Xojo 2018r1.1 and the Activate event does not exists in that window for none of the Canvas
I forget to mention: during the tests above, Xojo was the only running application. I learned earlier this year that Firefox and Xojo running together is a no-no (for me) (probably not enough memory: 8GB of RAM is not enough).
MacBook Pro (Retina, 13 inches, mid-2014), i5, SSD 256GB, El Capitan, Xojo 2015r1.
Is Xojo 2015r1 still able to run in El Capitan [10.11.6 (15G21013)] ? in Sierra ? High Sierra ?
I noticed a crash (a “relieable” crash) in a project running High Sierra.