This message was left at the bottom of his most recent Ci-en message on Jan 28th --
"
Miscellaneous notes
It seems that I will not be able to work for about 2 weeks, so the next post may be a little short. Comments may be delayed in replying ... I'm sorry ...!
Next time, I'll do my best to show more progress ...! "
Not saying its proof of anything because it really isn't but theres a bunch of reasons why people would stop posting on twitter/ci-en. For one, Twitter is a trash platform that bans you for anything spontaneously, i wouldn't be surprised if the stuff hes posted recently has earned him a ban.
Another couple of reasons are due to development. Some devs love to share their work, and i'd say that this dev is one such person but at some point you realize that you are spoiling literally everything you're doing and it's going to hurt interest if you don't hold anything back, finally and this is much more common -- alot of devs run into writers block or just randomly lose interest for a period of time. Its also possible that the dev is working at a furious pace and hopes to release the game soon and doesn't want any distractions.
These along with the usual reasons (unexpected eviction, expected jail, unexpected uunemployment, unexpected internet outage in your area) are all pretty normal. It really depends where you are working out of, not everyone is in or can afford Tokyo. Real life takes us out of our hobbies while we're fixing it. People who in the age group to make hentai probably aren't at risk to covid, particularly to recent strains of the virus.
Its far more likely that its a temporary, unexpected hiatus.