Incredibly cryptic error when running DB transaction

  const [newSolution] = await db.transaction(async (tx) => {
    await tx.update(csTable).set({ state: "archived" }).where(eq(csTable.state, "solved"));
    return await tx.insert(csTable).values([newCollectiveSolution]).returning(collectiveSolutionsPublicCols);
  });

  const [newSolution] = await db.transaction(async (tx) => {
    await tx.update(csTable).set({ state: "archived" }).where(eq(csTable.state, "solved"));
    return await tx.insert(csTable).values([newCollectiveSolution]).returning(collectiveSolutionsPublicCols);
  });

⨯ TypeError: value.toISOString is not a function
     at Array.map (<anonymous>)
     at Array.map (<anonymous>)
     at Array.map (<anonymous>)
     at eventLoopTick (ext:core/01_core.js:178:7) {
   digest: "617867408"
 }

⨯ TypeError: value.toISOString is not a function
     at Array.map (<anonymous>)
     at Array.map (<anonymous>)
     at Array.map (<anonymous>)
     at eventLoopTick (ext:core/01_core.js:178:7) {
   digest: "617867408"
 }