I too have had clients with IRS adjustments. When I review the tax return I find that the client received their stimulus through direct deposit and Lacerte is calculating an added tax credit for stimulus. The IRS is adjusting that added amount out of the "paid taxes" for your client, thus reducing tax payments by the errant credit. For example my client is married, no children,  income is below the required threshold for full stimulus payments. My client received two stimulus payments in 2020 as follows:

$2398

$1200

Lacerte added the $1200 as an additional tax payment thus overstating my clients payments by $1200.  The IRS caught the error and deducted the $1200.  The reason it was added had to do with my input of the payments into Lacerte. I put the first stimulus as $1,200 and the second as $2,398.  However,  it was actually the other way around, the first my client received was $2,398 and second $1,200.  The program calculated that my client should receive an additional $1,200 as the first stimulus is $2,400 for a couple at or below the threshold of $150,000.

The program thought the stimulus was short $1,200.00 and added it back as a tax credit. Thus the reason for the IRS adjustment.  Unfortunately, Lacerte should be looking to the overall amounts received as the two payments received were the amount they should have received, short $2.00. The stimulus payments by the IRS for the first distribution was $1,200 per qualifying taxpayer. The second payment was $600.00 per qualifying taxpayer. A qualifying married couple would be eligible for a grand total of $3,600.00 between the two payments. 

Hope this clears it up.