Rankings wipe-out in 24 hours due to products split. How to recover?

We wiped out 1 years of rankings progress (from average page ranking of 30 to 15) in 24 hours - av rankings crashed to 30 again and traffic has crashed more than 50% We know why. We split out 3 key product pages (each product page having up to 14 colour variants) into seperate products, each colour now having its own url / product page. We did this due to limitations on marketplaces like Shop App and TikTok Shop. Obviously a bad move in the short term but we can't go back to the old structure. What's the best way to recover rankings and traffic on the new product pages? We're on shopify. All new product pages (over 30 now instead of 3) were indexed really fast, and the old 3 product pages were de-indexed by Google. We did redirects from the old product pages immediately on migrating to the new structure but it didn't save them getting de-indexed. I don't think it's a question of backlinks as we never had ANY backlinks pointing to the 3 deindexed product pages. Our backlinks are mainly to the homepage. Any advice greatly appreciated. Sincerely hoping for a rebound.