A very strange issue!

I work a lot with Teams deployments for customers in my day job and have seen my fair share of strange issues. This issue has cropped up a couple of times and is definitely on the stranger side! In this post, I look at an error in Teams where the files tab does not work for a standard channel and all users receive the message “There was a problem reaching this app”.

Some context

I have only come across this particular issue a small number of times, and two of those times it was during tenant to tenant migrations. I’m not exactly sure of the root cause but essentially, when a user opens a Teams channel and selects the files tab, they are greeted with the message “There was a problem reaching this app” as shown in Figure 1.

Figure 1: “There was a problem reaching this app” in a Teams files tab

A very strange fix

When the issue was reported, the usual things were checked such as making sure the channel folder existed in SharePoint and that the Site itself had the correct permissions. Nothing there seemed out of the ordinary. This was also impacting all standard channels of the Team except the general channel…

I wanted to make sure that the channel was pointing to the right place in the back-end, maybe the migration tool had screwed up the folder references? I’ve seen something similar when a channel had been renamed but the folder remained the same…

To perform a quick check, I opened up Graph Explorer (aka.ms/ge) and signed into the tenant. I wanted to query the FilesFolder endpoint of the Channel. First I collected the Group ID of the Team from Azure AD, and then the Channel ID from Teams. You can get the channel ID by querying the Team but an easy way to get this quickly during testing is to open the Teams channel in a web browser and copy the Thread ID from the URL as shown in Figure 2.

Figure 2: Getting the Channel ID from the Team URL

From here, I issued a GET request from Graph Explorer for the FilesFolder endpoint as shown in Figure 3.

Figure 3: Issuing the GET request from Graph returns information about the channel folder

I verified the location in the response listed under weburl was correct and everything looked to be right. At this time, I realised the issue had gone away… only for the channel I queried! Very strange….

I decided to put this to the test and requested a few more channels that I knew had issues and to my surprise, they were all fixed after querying the endpoint. I can only guess at what actually triggered them to start working again but I suppose it’s possible the value is not present in the Graph until a query is run, at that point the files endpoint value may be calculated? I honestly have no idea but that sounds at least plausable.

Rolling out a fix

Of course, this fixed a set of channels but I didn’t want to use Graph explorer for every channel. I created the below script to use the Microsoft Graph PowerShell SDK to loop through all Teams that had a display name starting with “Migrated-“ (you can change this to target your own set of Teams as needed) and query the FilesFolder endpoint for each. After running this script, the issue was resolved for all impacted Teams.

Connect-MgGraph -Scopes "directory.read.all ChannelSettings.Read.All"

$Teams = Get-MgGroup -Filter "groupTypes/any(c:c eq 'unified') and startswith(displayName,'Migrated-')"

foreach($team in $teams){
    Get-MgTeamChannel -TeamId $team.Id | ForEach-Object {
        $Channel = $_
        $ChannelSettings = Get-MgTeamChannelFileFolder -TeamId $team.Id -ChannelId $Channel.Id
        $ChannelSettings
    }
}

Conclusion

I’m sure there’s a valid reason I saw this issue and it probably relates to the migration tooling but that is an investigation for another day. For now, I hope this post comes in handy for others who end up in the same situation!