Hello, I am only just joining this thread and I too am still learning things so take what I say as suggestions and feel free to correct me if I am wrong.
Firstly if you’re in the uk I just got a great offer of kaytee clean and cosy for £13 for 49l, which would do an entire cage or at least most of it. I made the mistake of getting the 24l one when I first ever bought it selling into the product advertisement saying “expands four times” what it doesn’t explain is it will come in a TINY packet. So I got the 49l one which is MUCH better. I think the price has increased to £16 now but still a good deal, there is always offers.
Kaytee Clean & Cozy Super Absorbent Paper Bedding for Cages, Hamster, Gerbil, Mice, Rabbit, Guinea Pig, 49.2 Litre, White
https://www.amazon.co.uk/dp/B007R6G8...CF1PRCD7?psc=1
Also I noticed you said you used three inches of aspen bedding? I may have misunderstood you as I think you were clarifying it’s depth in other areas but just wanted to quote this.
“ In most cases, it’s a good idea to provide your hamster with at least 4 to 6-inches of bedding
Scientific studies on hamster bedding have even found that a bedding depth of at least 15-inches can help improve a hamster’s overall health and well being. In that study, hamsters kept in cages with at least 15-inches of bedding had a healthier body weight, and they also exhibited less stress-induced destructive behaviors.”
Obviously 15inches is a lot but at least try and stick to 4-6inches for the entire cage. And I think you’d prefer paper bedding to aspen, it’s softer and can compact for them to make tunnels and burrow. I could be wrong but I believe it’s also more absorbent so spot cleaning becomes easier.
Also, I don’t know if it’s been covered but maybe the transfer into the bigger enclosure is stressful if you have the same number as enrichment from the smaller enclosure. It would leave a lot of open spaces and they like to have a lot of places to hide. It’s bizarre to show so much erratic behaviour because of a cage size increase. Also, again I haven’t read through the whole thread, but try to not switch between enclosures all the time as it can be stressful.
Hope I’ve helped and not repeated anything!