over 3 years ago - Shurenai - Direct link
Saves are not forward compatible between major versions due to too many things changing behind the scenes and even on the stage itself.

EG: An exp rebalance that reduces the exp needed to level up would result in you having more exp than is required for your next level; so you can never actually hit 100% of the exp required and gain a level, since you're at 101+% already.

EG2: They renamed the terrain block Stone to RawStone, suddenly your old save would have no stone layer whatsoever

And other such nonsense. If you want to continue your old save, you'll have to opt into the A18 alpha via the beta menu.