even here compared to other router models the 86u has the most topics about failed hardware, especially the 2018 batch. my main 86u was purchased in 2018 but it was from the 2017 batch and it's working fine. I then got another 2018 86u that had dead 5Ghz radios from the start. i replaced it and got lucky with another 2017 router that is working well for about a year now. i don't know about later batched from 2019 and up but it seems like if you have a 2018 router then your days are numbered.Many, many RT-AC86U's used by customers (and I had one myself). Rock-solid for the vast majority is a fair assessment.
The vocal few that do have issues just skew that perception.