It was updated and optimized to work with D2R Items

It was updated and optimized to work with D2R Items: Resurrected but remains rooted in 20 years-old technology. It's also having difficulty adapting to "modern player behavior."
"In 2001 there wasn't nearly enough content available on internet around the game of Diablo 2 'correctly' (Baal plays for XP and Pindleskin/Ancient Sewers/etc to the magic find, etc)," PezRadar said. "Today but, a new player can seek out the most amazing creators of content who can show players what to do in various ways.
A lot of them involve a lot of database load due to creating load, then destroying games all in a short time. Although we could have predicted this with players making new characters on new servers, and working hard to find their magical items, we significantly underestimated the amount of information we got from beta testing."
Another issue is the frequentity of global database saves, which are happening way too often for no good reason. Blizzard is making some tweaks in order to reduce the frequency of saves for the moment and is working on a more permanent fix, but it's sometime in the future because it's "an structure overhaul that will require time to build and test, before implementing."
At the moment, Blizzard is taking three steps to to make Diablo 2: Resurrected more easily accessible. Rate limiting this will place an upper limit on how fast and often players can start and join games; the establishment of a MMO-style login queue to ensure servers won't be hampered with a flurry of simultaneous logins; and splitting crucial functions into smaller ones.
But , these strategies could result in alienating a segment members of Diablo 2: Resurrected player base all on their own. For players who exceed limit on their rate, for instance are likely to receive an error message saying there's an issue with communicating with game servers.
That's really not much different from what they're running into right now (but it's expected to happen less often and to the smallest number of people) as login queues can mean that players will have long waiting periods before being allowed into the game. Both are far better over the current D2R items for sale console however, they're not going to do much to solve the many calls to end these problems completely.