Are these documents using templates to be created? I would delete and replace any templates as well.
To investigate the problem:
I would use "Send an HTTP to SharePoint" in a flow to look at the details of the document.
You will need to use multiple HTTP requests to look at the properties of the document as a List Item and look at the properties of the document as a File. See SharePoint Rest List Specific Item examples.
In SharePoint a Document Library is just a special type of List. So each document is a List Item and each List Item has a File. (A regular SharePoint List Items do not have File.) So you should look at the properties of both item and file.
Run the HTTP requests on the document before Flow1, before Flow2, and after Flow2.
See if you can see a change in the property or field DocumentType. Just like I did in this problem, I ran an HTTP request to look at the background data and recognized the problem.
Example HTTP Requests Below:
Here is an example file in my Document Library. The file list item ID is 588.
Document Library List Title: "Documents"
Document/File ID: 588
Documents - File Item ID 588
Here are multiple HTTP Requests to run on the file.
HTTP Requests have Different Outputs
Each HTTP Request uses the Headers to determine how much data is returned:
- Accept application/json;odata=verbose
- Accept application/json;odata=nometadata
Verbose is all data which is good to see what is available. Nometadata will trim some of the extra options off.
The GET Uri for item:
_api/web/lists/GetbyTitle('Documents')/items(588)
The GET Uri for item properties:
_api/web/lists/GetbyTitle('Documents')/items(588)/properties
The GET Uri for the item fieldvaluesforedit:
_api/web/lists/GetbyTitle('Documents')/items(588)/fieldvaluesforedit
The GET Uri for the file:
_api/web/lists/GetbyTitle('Documents')/items(588)/file
The GET Uri for the file properties
_api/web/lists/GetbyTitle('Documents')/items(588)/file/properties
Here is a screenshot of each of the HTTP Requests:
Item - HTTP Request
Item Properties - HTTP Request
Item Field Values for Edit - HTTP Request
File - HTTP Request
File Properties - HTTP Request
I would use these HTTP requests to look at the document before, during, and after the flows. Then check the outputs to see if you recognize any differences or issues with the properties. You want to focus on the specific field/property DocumentType.
I'm sorry I don't have the answer to your problem, but I think viewing HTTP requests as the document goes through different phases would give insight to the problem.
It is probably something silly like a blank value or property name and choices not corresponding.