Looking at your root photos, yes, those plants are definitely root bound. You can see the roots circling the perimeter and compacting densely that’s the classic sign. At week 5 in veg, an 8L pot is borderline for photoperiod (okay for autos, tight for photos). The lockout symptoms you’re seeing are partly root bound, but also pH-related. You corrected to 5.6, which is actually too low for soil soil prefers 6.2–6.8. At 5.5–5.6, you’re locking out calcium and magnesium, which explains the stunted growth and deficiency signs even though nutrients are available.
Don’t prune roots just transplant up. Move to a 12–15L pot with fresh soil (or top-dress with compost), and dial pH back up to 6.5 when you water in. The fresh medium will reset things, and the extra space will let roots expand. Root pruning is stress you don’t need right now.
Once in the bigger pot, your growth should accelerate immediately. The combination of root space + correct pH is the fix.
You’re not doing anything wrong — just learning the timing. Most growers upsize earlier, but you caught it. Do it now before flower.