The new redstone signal for lava cauldrons in snapshot 20w45a lacks parity with Bedrock Edition. In Bedrock the signal strength is 3, not 1, according to MCPE-104824.
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It's conceivable to me that what was intended was to add lava cauldrons with some signal strength for parity, but the value of the signal strength was not compared with Bedrock. In other words, the signal strength of 1 could be a dummy value just to give it a value, while the fact of a signal is all that was intended.
For comparison, when Bedrock got trade discounts for curing zombified villagers in the 1.15 betas, it initially made every trade cost only 1 emerald. That didn't mean it was intended for trade discounting in Java to make every trade cost 1 emerald.
Further info: In BE the signal strength of 3 for filled cauldrons is based on cauldrons being able to hold 3 levels of water. Each use of a water bottle on a cauldron fills it 1/3 of the way and increase the signal strength by 1. The signal strength of 3 for a lava cauldron indicates the fact that the cauldron is full.
Java value need to be converted to the Bedrock one, since it looks like a full cauldron, and even if there can't be used bottles, the lava fills the entire cauldron.
The changelog says, that the signal strength is 1 https://www.minecraft.net/de-de/article/minecraft-snapshot-20w45a, so this should be intended.