While the official fronts of Taiko no Tatsujin remain silent, it is from the Taiwanese arcade importer and agent Sume that we get this emergency breaking scoop. Remember them before we have the official Asian ver. Facebook page? (And before you ask, yes we are seriously considering reusing this lede pattern over and over until Namco steps up their game in talking)
But yes, after receiving the heads-up, Sume has swiftly published statuses on their Facebook page regarding connection errors that disabled access to online functionalities in Asian ver. AC0 cabinets since April 11 2018 resulting from server upgrade work. While there is no estimated time of resumption, Sume was promised that Blue ver. firmware would be pushed forth with the hotfix to the connection problems. For now, keep your eyes peeled from the above two sources of information for further updates.
Genuinely hoping that it is some significantly new stuff that botched things up for Namco...