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Security1 distinct publisher2 min readPublished
Two Teams faults are open at once: Mac users cannot join calls, and Windows clients can take up to two minutes to launch. With the code-change theory withdrawn, there is nothing to plan a fix date around.
The Watch · Security desk
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A ticket that says Teams will not start on Windows has two documented causes this week, and only one of them lives on the endpoint. Microsoft confirmed on Tuesday that Windows security updates released since the August 2026 Patch Tuesday cause crashes and launch failures in Teams and the new Outlook [9]. The other is the load fault Microsoft is still tracing through service logs and telemetry, having reached out to affected users to find the cause [1][4]. The reflex on a busy desk is the same in both cases, which is to pull the update, and in one of the two it removes a patch and fixes nothing.
The Mac fault is the one with a moving explanation. Microsoft first attributed TM1466659 to a code change that left the Teams call and meeting service infrastructure unable to process some requests [5][6]. Further review found that may not be the cause [7]. Microsoft now says it is "reassessing our root cause understanding and reviewing service logs to isolate the source of impact, so that we can determine our next steps regarding impact remediation" [8]. A code change has a shape an admin can plan around, because reverting it produces an estimate, unlike log isolation, and both advisories sit at determining options rather than shipping a fix [4][8].
Take Microsoft's own upper bound and do the arithmetic: two minutes on a first launch, once per user per day, means 100 affected Windows users absorb 200 minutes, or three hours and twenty minutes, of waiting for every day the issue stays open [2][12]. That is the part of this that shows up in helpdesk volume rather than in any security log.
No CVE and no actor apply here; this is purely an availability problem. What makes it worth tracking on this desk is the patch-compliance pressure created by the Tuesday crash bug, which gives every user with a slow Teams launch a plausible reason to ask for a security update to come off their machine [9]. That request is answerable only if the desk can tell the two Windows faults apart, and Microsoft has not yet named the cause of the second [1][4].
Microsoft's advisories for the week cover the Windows launch delays, the Mac join failures, the update-induced crashes, and an Exchange Online condition throwing "Server busy" errors and delaying mail to and from external domains [10][13]. Microsoft's published avoidance advice, the web client or the Teams mobile app, attaches to the Windows launch issue [3]; the Mac advisory offers reassessment and next steps [8].</body_markdown> </invoke>
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Microsoft is working to resolve a known issue that causes delays or blocks some users from opening the Microsoft Teams desktop client on Windows systems.
Microsoft said that when first opening Microsoft Teams on Windows devices, some users may be initially unable to load the client or may encounter loading delays of up to two minutes.
Microsoft said affected users may be able to avoid impact by using Microsoft Teams on the web or alternative access methods such as the Teams mobile app.
Microsoft is still analyzing service logs and telemetry data and has reached out to some affected users to identify the root cause and determine mitigation options for the Windows launch issue.
Microsoft is separately investigating an issue preventing Mac users from joining Teams calls and meetings, tracked as TM1466659 and confirmed on Thursday at 10:57 EDT.
Microsoft initially blamed a code change for causing the Teams call and meeting service infrastructure to fail to process some requests.
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1 article · September 4, 2026
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Vendor advisories, quoted accurately
Every statement in this story is Microsoft's own, taken from admin-centre advisories and quoted by BleepingComputer; no affected customer and no outside monitor appears anywhere. What keeps this thin rather than merely single-sourced is that the vendor has already reversed itself: the code-change explanation for the Mac join failures was withdrawn on further review, so the diagnosis underneath the quotes is still moving.
Scope never quantified
Impact is given as "some users" and left there. No seat or tenant counts appear for any of the four faults, and nothing indicates which regions or which Teams builds are hit, so there is no basis for measuring how far any of this reaches.
Slightly ahead of what is known
The reporting stays inside Microsoft's hedges, which is why the gap is small. The stretching is ours: the two-minute ceiling scaled to a hypothetical hundred users yields a tidy three-hours-twenty of lost time that no disclosed population supports, and counting four faults in one week suggests a common thread that nobody in this story has looked for.
The broken vendor is the only witness
Microsoft controls both the wording of the impact ("some users") and the timing of when a root cause is announced or unannounced, and it is the sole voice quoted. The page also closes with a sponsored pitch for a security vendor's simulation report, unconnected to the outages but part of how this reporting is funded.
Faults confirmed, cause and size open
Confidence sits low because the vendor is the only witness and one of its conclusions was retracted while the story was live. The paper trail itself holds up: advisory TM1466659 carries a timestamp, and the remediation language is quoted directly, with Microsoft naming its own workaround. So the existence and shape of these faults are dependable even where cause and scale are not.