Can an individual work both as a W2 employee under one company name and work as LLC - 1099 status under another company name at the same time with both companies being run and owned by the same individual. Both companies are incorporated as "S" Corps and perform the same basic service for their clients?

“Can an individual work both as a W2 employee under one company name and work as LLC - 1099 status under another company name at the same time with both companies being run and owned by the same individual.Both companies are incorporated as "S" Corps and perform the same basic service for their clients?”========> For the same ER and same job. It's technically possible, but not both for the same job. You'd really have to have separate sets of duties and conditions for the 1099 work than for the W-2 job. A 1099-Misc is for contract work. No taxes are withheld and contract work means you had no set hours, supplied your own tools, didn't need supervision, etc. Contract work can include any money paid to you for expense reimbursement.
A W-2 is for reg EEs. It includes everything you were ever paid, including moving expenses, bonuses, severance, excess or unaccounted expense reimbursements, fringe benefits such a leased car, etc. The company can't pick and choose what goes on the W2 subject to soc sec tax and what doesn't.It's extremely rare that you start out as a legitimate contractor and then switch to being an employee, but that would be the rare instance where you legally get both a 1099-Misc for the work done as a contractor and a W-2 for the work done as a reg EE.