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The UK provides an instructive example of the administrative challenges of distributing means-tested tax credit benefits on a monthly basis. In 2003 they implemented a big Child Tax Credit and Working Tax Credit. The design is in many ways similar to current US proposals
Immediately, they ran into major overpayment problems. About 1/3rd of all benefits were overpaid, and there were reports of confusion and hardship as people had to pay back welfare debt at the end of the year
Policymakers admitted that they were blindsided by how many changes in circumstance people had over the year
To address this, they implemented a large income disregard. This cutdown on overpayments, but at the expense of accuracy and horizontal equity (people with the same annual income could get different amounts depending on where they started)
As austerity came after the financial crisis, they reduced the income disregard again, and the overpayment problem came right back. But by this point the tax credits were slated to be replaced by Universal Credit. So they never really solved the problem, they just sort of gave up
