This has probably been answered many times before, but I can only see thing on taking breaks from training rather than riding during a breaks. I was three weeks into SSB1 when but we’ve just taken a 2 week holiday in the Lake District so doing lots of climbing with vo2 max work and long periods around my outside FTP, total TSS wasn’t silly high (500ish) it just wasn’t really structured 1 – 3 hours of riding. Coming back do I re-start SSB or continue from where I left off? I have a couple of weeks of slack in my plan to hit my A race
I guess the answer depends on how you feel. If you’re feeling fairly rested then I’d probably just pick up where you left off. If not, then maybe a week of gradually building up intensity and then picking up where you left off the following week. I don’t really see the benefit of completely restarting SSB as it sounds like you will have been continuing to build (or at least maintaining) your base while on holiday.
I’m no expert though and others may give you a more reasoned answer, but the above is what I would do in your position.
I don’t know why anybody, short of sickness, would want to restart ssb. It sounds like you were doing some great rides! If you’re rested, I’d say go for it. If you’re tired, maybe take a recovery week first. Save the rest of your flex weeks for later.