.strm files play without issue when my iPhone is connected to the local LAN (WiFi) but fail when I try to play them remotely over cellular. I found a similar post from earlier on in the .strm Beta but replies there suggested it was a bug which was fixed at some point. However, it seems there may be a regression/reoccurence of this bug. To confirm this I created 'All Quiet on the Western Front (1930).strm' containing the exact URL to the .mp4 mentioned in the earlier post and it worked fine on WiFi but failed over cellular with roughly the same error the OP received:
"The connection to Channels DVR Server had a problem. Press play to try again. (Transcoder) Couldn't probe recording: /Volumes/DVR/Imports/Movies/All Quiet on the Western Front (1930).strm"
Also, just as the OP I tried setting cellular streaming quailty to Original to attempt to bypass the transcoder but it failed with the same error. This should be fairly easy for anyone else with an iOS device to replicate for further troubleshooting but please let me know if I can provide anything additional if it helps identify/remediate this bug. I am still on iOS 18.7.2 using Channels 7.0.1, but I can upgrade to iOS 26.1 if it would help (just been putting it off as I have heard from a few folks that Apple was still working out all the kinks with it). Thank you for your support.