It's always something in this HiFi hobby. Like being excited and waiting in anticipation of your new tubes breaking in, and an unrelated tube failure happens.
Maybe Linlai will expand their production, they haven't been in business very long and I think they want to excell in their current offerings. It may also be due to the design team that started the company. This may be their area of expertise.
Regarding fluctuations during the burn-in process, this is not the norm but does happen. I like how most true NOS tubes burn-in, as the hours pass you keep hearing improvement.