There's random and there's random. I often maintained that this could be a distant connection; a handyman, a repair men, someone they hired to help out from the area. A local that might have a hidden drug problem. etc. They were very trusting people and embraced living in a gentrified area with incidents of crime, including murder and an 8 year-old shot within walking distance while they were there. Such a person would also possibly have access to and familiarity of the home.
As to your initial query:
1. Door "Smart" lock glitched open, people going up to check on open doors as they do in many neighborhoods checking if car doors in driveways are open (as many see on Ring community).
2 .Door "Smart"lock defeated. Someone posted an earlier model of that door lock hacked with a paperclip. This is all over the internet and common skells know this. Maybe someone who knew this was picking houses out with a smart lock of that kind.
3 .Rear door left unlocked. Tired couple with young kids let the golden doodle out and forgot to lock it. As security oriented as I am I had lapses when I had little ones and was constantly in brain fog as most young parents.
4. Egress window. Rear egress window from the yard into the basement. Some of these models which prioritize egress (legal code requirement) can be pried open with little disturbance (hence no apparent forced entry).
I can probably think of a few others. When I lived in NYC the locals were crazy creative with these things. Ah, the thing's I've seen.
As for your other points you're telling me you are not familiar with burglars. You can adjust to the dark, you can use a flash-light and cover it, you can be stupid and brazen like tweakers, the house was 2,500 sq ft max. This isn't that difficult. Plus things obviously would have went south in this scenario, so it's not like it was well planned out even in that case, which is what we see in these cases. Nothing is reported missing in a lot of attempted burglaries when a tweaker freaks out, shoots impulsively, and high-tails it out of there. Happens a lot. Furthermore, the police state nothing was "apparenly" missing. etc. When doing press releases, updates in an ongoing investigation, there is tolerance built in the language 'cause often times they don't know. Could be with the 5 year wedding anniversary Spencer bought an expensive small gift that was a surprise and most of the friend circle interviewed didn't know. A handyman, repair person might have caught wind of it and that's enough motive for someone down on your luck and it would seem nothing was stolen.
Of course, I still maintain a lot of other possibilities, but to dismiss this very plausible scenario given the location and crime history of the neighborhood seems lacking.