Baffled by sudden urinating

I have an almost 6 year old chihuahua/small breed mix. We adopted him as a puppy and he has been completely housebroken since he turned 1 year. In the past week, he has started urinating on the floor 4-5 times a day. He has been to the vet twice. Urine (twice) and bloodwork all look reassuring. I'm guessing it's anxiety, but I'm completely flummoxed by the pattern of urinating and how to fix it. I'm open to suggestions, thank you!

• This all started the same day my husband left on a work trip. However, my husband is a pilot and leaves on work trips every other week. This has been the case since we got the dog, so it's not something new. Obviously this is something we can't change. Waiting to see if he stops this behavior when husband is home in a few days.
• Urinates only in the downstairs on the hard floor. No accidents upstairs on carpet. No specific spot he is peeing. It's just on the floor not on things.
• Urinates within 5 minutes of me leaving the room. He is not locked or gated off downstairs. He could absolutely follow me! I'm talking I run upstairs to use the bathroom or switch the load of laundry and he pees. I've set a timer, so I know the 5 minutes is accurate.
• When we're in the downstairs with him, he still goes to the back door and signals to be let out. I've been ensuring that he actually urinates when he goes out. However, he has peed on the floor even with having gone pee outside within 30 minutes.
• Goes all night (~12 hours) without peeing. Still comes to wake me up and runs to the door to go out and pee first thing.
• Does not pee when we leave the house. I've been gone 3-4 hours each day this week and he has not urinated once while I'm gone. It's only when I'm home.
• We do have two small kids (3 years and 12 months). But I can't think of anything new with them. Both kids have been mobile for a while. They are never unsupervised with the dog. He absolutely adores them and sleeps in my 3 year old's room every night.
• If it wasn't for the peeing, I would not see any sign of separation anxiety. He has been better behaved this past week than he normally is (less barking and less whining than his norm). He has been affectionate and snuggly.
• Again, normal bloodwork, negative for UTI. Vet suggested limiting his water intake, but I've already done that.
• He is crate trained and often retreats to his crate in our room. But with this pattern of behavior and with chasing two kids around, he would end up being crated a large amount of time as we go up and down the stairs frequently.
• He has plenty of chewers, peanut butter mats, etc. Plus more treats than he should because the kids love to feed him.