You're right that this is PS 7-specific behavior. The progress renderer was reworked in PowerShell 7.2 — progress output now renders through PSReadLine and the renderer coalesces/throttles repaints instead of redrawing on every record. When you mark a bar -Completed and then immediately open a new bar with the same -Id, the renderer sees a record for an Id it just cleared and can skip the repaint entirely — hence "works if I add a delay, but not without one." The delay gives the renderer a tick to actually process the completed record before the new one arrives.

The cleanest workaround is to use a distinct -Id for each progress sequence (the -Id is only needed to correlate -CurrentOperation/percent updates with the same bar, so there's no downside to a fresh Id per stage):

Write-Progress -Activity "Testing1" -Id 1
Start-Sleep 5
Write-Progress -Activity "Testing1" -Completed -Id 1
Start-Sleep 5
Write-Progress -Activity "Testing2" -Id 2     # new Id -> always repaints
Start-Sleep 5
Write-Progress -Activity "Testing2" -Completed -Id 2

A few related notes:

• If you don't -Completed the first bar, the second bar does show without a delay (as you observed) because the Id is still "active" — another reason the same-Id clear-then-reopen is the trigger.
• Renders are also throttled internally (~100ms window), so very rapid Write-Progress calls in a tight loop are intentionally coalesced; you typically only notice when a bar opens and closes within that window.
• In scripts, a robust pattern is to compute progress once per iteration with a single -Id per task and always emit -Completed before return/break, letting the renderer settle.

This is worth reporting as a bug if you'd like it fixed — the repro is minimal and it's a clear regression vs. 5.1. In the meantime, unique -Id values per progress bar avoid it completely.