In my case I disable auto join on all and they’re all back on in 4-5 minutes.
I was also able to verify this as the device will still really connect to the “disabled” hot spots, even after switching it off. Just took a while for the profile to resync.
Edit: only 5 of 9 re-enable auto join after I disable it.
Looks like comcast xfinity type networks are being imposed too. The xfinity App may be toggling these XFI, Xfinity Mobile, xfinitywifi pieces your way too.
The Xfinity hotspot service typically has two SSIDs going: "xfinitywifi", which is unencrypted and has a captive portal to log in, and the "XFINITY" network, which the installing the profile enables access to and which is encrypted with 802.1X authentication.
For everyone except apparently the carriers, Apple is very strict about the opt in nature of managed WiFi networks.
> even after switching it off
This might be your issue, because after a restart your iPhone no longer has access to your saved Wi-Fi credentials, but it can still use EAP-SIM to join T-Mobile's Wi-Fi network first. But I see your point that it does not respect the "Auto-join" toggle.
If this happens often enough to annoy you, you could file this bug with Apple by typing "applefeedback:///" into Safari. It could take some guesswork to figure out what component to file this against.