Thank you for the reply. I have contacted Woo Audio through their website to ask about warranty service / next steps. This may turn out to be a good chance to test the RMA process. I have only recently gotten into Woo Audio products, so I have never had a chance to work with their support, but from everything I have heard / read about them, I am optimistic it will go well. I will report back here on results of the process.Regarding instead your issue with the SE/BL switch on the Tube Mini I've touched/tested/switched it while playing through the BAL output and have had none of the issues you're experiencing, no drops or crackles or channel interruptions so you probably have a defect on your cable or your unit would need to be seen by Woo Audio, it's definitely an inconsistent behaviour for the Tube Mini given its exceptionally high manufacturing quality, sturdy build and brilliant engineering design implementation. I would first try an upgrade cable like the Forza Audio Works Noir HPC before sending it back to Woo Audio although you could reach out to Mike at Wood Audio who has always been very responsive and he might advise better.
Also, a potentially unrelated wrinkle, but maybe worth mentioning if it seems noteworthy to anyone. When I received the unit it was new in its box with what appeared to be an intact factory seal, but the USB adapter was not present anywhere in the box / carrying case. I have replicated my issue with the switch using both the Apple USB-C 4K A/V adapter for the iPad and iPhone as well as with plugging the device directly into a USB-A port on my desktop computer, so I don’t think it was due to the missing cable, but it makes me feel like there was just something up with this unit from the beginning. It also occurs with multiple cables from different brands and multiple sets of headphones, all of which work fine with other amps / dongles. I purchased it from headphones.com - and I have always been pleased with the quality of their products and their service - this is the first issue I have encountered with something from them. I wrote to them about the missing cable, and within a few hours I got a notice from Woo Audio that they were shipping an adapter directly to me - arranged by headphones.com. The whole experience just seems a bit odd relative to the high quality of Woo Audio products and their good reputation, so just sharing in case anyone has insights that spring to mind. I hope to be sharing more info about a quick and effective RMA process shortly! In the meantime, I’ll still be rocking out to the WA22, which has been a flawless performer and came with all of the accessories as advertised.