If the number of Smyles in your wallet looks lower than the total you've earned, this is completely normal, and here's the reason behind it.
Each month, you can add up to 15,000 Smyles to your wallet. That's the amount available to spend on rewards. If you earn more than 15,000 Smyles in a month, the extra still counts, it's just not added to your spendable wallet.
Those additional Smyles aren't wasted. They still contribute to the leaderboards and to any challenges you're taking part in, so your effort is always recognised, whether or not it lands in your wallet.
In short:
Your wallet holds up to 15,000 Smyles a month to spend on rewards.
Everything you earn beyond that still pushes you up the leaderboards and counts towards challenges.
So if you've had a really active month and notice your wallet has capped out, it simply means you've gone above and beyond, and all that extra effort is still working in your favour on the leaderboards.