Compiled Project strange behaviors

This is related to a Desktop Standalone application that is ListBox based.

I do not know why, but recently, I loose the Active Cell when going from that application to another and back (because I am populated a document with data taken in a different application/window (Firefox in that case).

Some days ago, I decided that it was the day to gain back this feature (thank you Norman for that tip, years ago).

After some search, I commented a set focus line, tested and gain the feature back. THAT WAS THE ONLY CHANGE.

I compiled the application, used it a bit, realized the hour (late at night) and went to bed.

Now, in the early morning (no rain), I wanted to complete the data “move” and fired the application, take the (local) web page and started.

Ba-da-boom !

I lost the “change to the new Row / Edit that Column”:
The Row change works fine (a key press into the down arrow), but I loose the Column #: Column(0) is now Edited instead of Column(4).

This erratic behavior is particularly unpleasant and I don’t know what to think about it.

Moreover, where to look?

Is Xojo sensitive to the lack of available memory (RAM)?

Should I restart, only launch Xojo, Compile, shutdown, restart, launch my app, Safari and work like that?

I’m going to try.

PS I have several apps running, and haven’t restarted my MacBook i5 since yesterday afternoon.

Nota: I had unexpected reboot (and loose work) while I was running High Sierra, so I went back to El Capitan.