No it doesn’t. All it means is that an amendment to an amendment making that explicit failed to pass. Despite that failed amendment within a failed amendment, the Supreme Court still found secession to be illegal.
1st) In 1869??? That’s AFTER the fact - RIGHT after the fact, with stacked courts. What did people think all before this war?
2nd) Again, what about the Constitution? There is nothing in there. Case law is the trend of Progressives, instead of reading the Constitution itself for oneself. Interpretations can be very wrong.
3rd) Who cares if it’s failed or not? Irrelevent. The point is, someone felt the need to explicitly mention it in amending the Constitution. There had to be a reason for that.