Wow, I posted this question some time ago.
Over the years I've tried most (or probably all) the steps below. I'm actually no longer at that job and my new job has much better WiFi, however, sometimes sending pictures or whatever is still quirky regardless if I'm on WiFi, 5G, or between both. At this point, sending pictures seems to have improved (unless I have poor reception while on 5G), so I haven't worried about it much.
My friend hasn't complained about duplicate text messages for some time. Maybe once or twice, but think he had an app running in the background because he's the only person to ever complain about this.
In any case, my iPhone X has been doing weird things lately and sense it's time for an upgrade soon. First thing is I've noticed the battery level drops quickly. Usually it's fine all day, get in my car, drive home, and it drops like a rock during my commute. I attributed this to cold weather, but this is new (unless I left the phone in the cold garage while doing work on my car). When the battery was dying quickly with my iPhone 3GS, I replaced the battery myself thanks to Ifixit, but believe this phone is much more difficult and just not worth it since it's old.
The latest quirk has been my email notifications haven't been dinging or showing. The phone did an update early last summer, and, without changing any settings, no more email alerts. I tried all the tricks I found online, restarted the phone, etc... Some suggestions have been to reset the phone (not happening since I'll lose everything) or deleting my email account and reactivating it (also probably not happening since I may lose all my emails).
In any case, most of these quirks haven't been an issue and confirms what I've said for years: Apple devices does what they want to do when they want to.