I think sea launched missile failure is far more common than you’d think. My father launched a Polaris one fifty years ago and it went off course and had to be self-destructed. Apparently that wasn’t unusual.
If your test are not successful it's not longer a deterrent so best not test. If it all kicks off it won't matter to us if it fires or not, we'll be too busy being dead or living like mad max.
Good to know the tens of billions we are spending on a nuclear deterrent is worth it.
This was the second test in a row that failed. The last one was in 2016, so they had a bit of time to work out the issue and get it right.
Also
https://www.theguardian.com/uk-news/2024/feb/21/labour-seeks-trident-assurances-after-missile-test-anomaly