Apollo data goes stale within weeks, not months. I ran a campaign in May with a list I built in February and reply rate was under 1%, rebuilt the same ICP fresh and hit around 4% with identical copy. So if your Snov campaigns suddenly dropped, check when you last refreshed the list before blaming the sender.
On LinkedIn, the bans are real but mostly hitting people running 100+ connection requests a day or using browser-based scrapers. If you're at 20-30 invites a day from your normal IP you're probably fine. Dedicated cloud-based tools are where people get flagged.
Also worth checking your domain health on something like mxtoolbox. Could just be deliverability creeping up on you after 9 months of sending.