@David-TP
Hey
Haven't yet swapped SIM-cards with Deco and mobile phone, but there was happy situation during whole weekend (23th - 25th Aug):

This started last friday (almost 9am), while checking Deco-status via mobile phone, while in the work place...
Lasted whole weekend maintaining 5G-connection, only to lost it during last night.
Checked few times my internet providers, DNA, web site and found connection map, including markers for "planned upgrade works" there...
Did send question about upgrade marked near my location, not yet have answer for that...
Also, got into my mind an idea that I saw a log there in Deco control site (via PC) and opened it, did read it as long as it gave me something...
Lots of lines, repeating:
user.err : [mobile] [DebugThreadStackSize] Memory status statistic file open failed.
user.warn : [mobile] [GetEventType] qmi_module=1, qmi_msg_id=0x0051
user.warn : [mobile] [PostEvent] Event (id: 0x00000000, type: 0x10000001) return directly.
user.err : [simplecom_helper][qeng_servingcell_cmd_handle]:+QENG: NR5G-NSA or NR5G-SA not found.
Not sure if those are anything "not normal" or so...
Did not check what it said while 5G-connection was found and maintained... Just today got an idea to check what log have saved on it.
Saved today's log, as 5G connection was lost, probably when day changed or during late night/early morning... So I can send it if needed.
I also recall seeing red light on Deco, just while waking. Not sure if it just normal to Deco to do that while idle and day is changing, or if something was going on with connection provider's services... However I think it happened somewhere around morning 4am - 5am, and had left my PC on.
Update:
After this comment, I swapped SIM-cards in Deco and mobile phone...
Did some testing.
Nothing different there, mobile phone gave similar speedtest (Ookla speedtest) results with both cards.
However, after I put SIM card meant to Deco back to it, 5G-connection was once again found by Deco...
Got new logs saved in file.
If needed or/and wanted to checking, I can provide them.
Note:
While reading new log lines, I noticed something weird:
Thu Jan 11 12:35:02 2024 user.err : [mobile] [DebugThreadStackSize] Memory status statistic file open failed.
Mon Aug 26 14:28:13 2024 user.warn : [mobile] [GetEventType] qmi_module=1, qmi_msg_id=0x0082
Between these lines, SIM-card was removed to testing it in mobile phone...
It changed from Mon Aug 26 to Thu Jan 11 