.h no such file or directory.

I am developing an object/library for later use in a project.

My development project has the basic .ino file. I have added to additional TABs

One is named XXX.h and the other one is named XXX.cpp

They both appear in the tab list, and they both appear to have contents.
I have saved the project, and downloaded a copy of the project for recovery.
I do a save and download every time I make changes. I learned not to trust
your software.

I NO LONGER TRUST THE SAVE OPERATION. I HAVE BEEN BURNED MANY TIMES BY THIS
TYPE OF ERROR. All of the recovery actions, thaI can find to recover the missing file seem to be for the local editor version, not the Online Create version, NOT A GOOD SITUATION. All of the problem I have found similar to this indicates the problem has been fixed. I don't think this is the same situation.

I have a UINO board plugged in when I do the verify compile. My development is not far enough to load
into the board.
Running UBUNTU 17.10 Current Chrome (linux) browser. And I believe I have the current Arduino Create Agent.
I have had this problem earlier. At that time I reinstalled everything. That did not stop it from reoccurring.
I am finally frustrated enough to file a bug report.

When I just try to compile (verify) I received the message

"XXX.h no such file or directory" (the XXX is a substitution, it represents all of the projects in which this occurred)

The error message references the line my my "#include".
That line reads: #include "XXX.h"

Just a few minutes earlier the compiles were finishing with or without errors.

I have encountered this before. If I log-out or just close the browser
the next time I log-in and reedit the project the named file is listed in the
tab listing. But its contents is empty.

At that point I just go into the downloaded copy and recover the missing file.

I am sorry, but I can not recreate this error at will. But it is occurring enough
that I have taken actions to prevent the loss of data.

You should be aware of this problem. I would like a problem opened for this situation.
If not, at least I warned you.

I do not feel this is a problem with my individual project. It has happened too often in
my other projects. That is why I listed it in this forum.

Now I will go out and delete and recover this project.

It sounds like you're having the same problem as this person:

Create editor is not ready for prime time yet, as far as I can tell. It seems like basic functionality isn't totally nailed down (like this). I would suggest avoiding it for now and using the normal IDE.