It appears to largely be a manipulation / changes in the reporting -- Here's the FAQ attached to the report:
https://www.bls.gov/cps/employment-situation-covid19-faq-may...
> In the establishment survey, workers who are paid by their employer for all or any part of the pay period
including the 12th of the month are counted as employed, even if they were not actually at their jobs.
> The household survey is conducted by the Census Bureau and normally includes both in-person and telephone interviews, with the majority of interviews collected by telephone. Interviewing for the household survey began on May 17th, 2020. ...
> In May about three-quarters of the interviewers at these centers worked remotely to collect data by telephone.
> In April, BLS made changes to the establishment survey net birth-death model used in the estimation process. These changes were continued in May. However, after further research, BLS extended the estimation modifications back to March. This change contributed to the revision for March.
> During their review of household survey data for May, BLS staff tested for outliers to determine
whether any changes were needed to the seasonal adjustment models. BLS staff determined that, as in
April, the vast majority of household survey data series had significant outliers in May. Therefore, BLS
staff made adjustments to the models used in seasonal adjustment processing to better account for these
outliers.
> Of the 8.4 million employed people not at work during the survey reference week in May 2020, 5.4
million people were included in the “other reasons” category, much higher than the average of 549,000
for May 2016–2019 (not seasonally adjusted). BLS analysis of the underlying data suggests that this
group included workers affected by the pandemic response who should have been classified as
unemployed on temporary layoff. Such a misclassification is an example of nonsampling error and can
occur when respondents misunderstand questions or interviewers record answers incorrectly. BLS and
the Census Bureau are investigating why this misclassification error continues to occur and are making
changes for the June collection. (See item 14 below.)