Sorry to post repeatedly ...
I think I understand what's going on.
When I click to attach files it opens directly the default Documents UI (I use Pixel Experience 8.1.0). And when I select some file from the memory card I get error.
I decided to freeze Documents UI.
Now, when I click attach, it opens a popup with options (attached screenshot). And I succeeded in all the tests (about ten attempts on different topics, including the MiXplorer), always selecting the same file stored on the memory card. In all tests I used MiXplorer to select the file.
Conclusion. I think my bug is not related to XDA Labs itself but to the Documents UI of the Pixel Experience. However, no errors related to Documents UI appear in the logs.
Now a request: could you force this selection popup before opening Documents UI directly?
I do not intend to keep it frozen, it might not be a good idea.
I think I understand what's going on.
When I click to attach files it opens directly the default Documents UI (I use Pixel Experience 8.1.0). And when I select some file from the memory card I get error.
I decided to freeze Documents UI.
Now, when I click attach, it opens a popup with options (attached screenshot). And I succeeded in all the tests (about ten attempts on different topics, including the MiXplorer), always selecting the same file stored on the memory card. In all tests I used MiXplorer to select the file.
Conclusion. I think my bug is not related to XDA Labs itself but to the Documents UI of the Pixel Experience. However, no errors related to Documents UI appear in the logs.
Now a request: could you force this selection popup before opening Documents UI directly?
I do not intend to keep it frozen, it might not be a good idea.