They changed the system.
"Notably [chages], the randomized block reward feature will be enabled at block height 9497418 (approximately 7–10pm Mar 10th, 2021 PST). While all nodes will still earn the same TFUEL earnings they would have before over time, it means there will now be significant variations in the timing and size of TFUEL rewards. This was necessary as usage of the Theta blockchain continues to grow, and in particular the number of Guardian Nodes staking. With 2,500 Guardian Nodes operating and goals to expand this to 10x that figure in the future, the number of transactions used for paying out TFUEL rewards with every checkpoint will continue to grow linearly. This new method eliminates the issue of scalability in GN rewards. .
At each 100 block checkpoint, there will now be 200–300 stakers randomly selected (weighted by their stake) to divide the block rewards. This is a change from the status quo where ALL stakers received a block reward at every checkpoint. The net effect is that instead of getting a small TFUEL reward every ~12 minutes, you will earn larger TFUEL rewards but at longer, non-regular intervals."