Soli filed an 8K on January 6, 2020 stating that the former auditor "has not expressed an adverse opinion or a disclaimer of opinion,...", meaning the firm had not resigned because of finding any discrepancies, although they did express concern about the company being able to financially continue operations (standard CYA statement, considering debt and cash flow).
Subsequently, they issued another letter asking for written permission to disclose information to the new accountants so they could assist them in the transition.
Finally, they wrote a letter certifying they had no disagreement with the statements SOLI made in the 8k filed January 6th.
So, here are my thoughts. Through 2018, the prior accounting firm would be on the line if they certified financials with inaccuracies or improprieties. 2019 was unaudited, so they could accept any information given them by SOLI and not have to take responsibility for the veracity of the financial statements. As an example, I had a client who I was certain was shutting off the cash registers before closing time and not including any of his business's sales that came after that. But I was not auditing him, so I was obligated to prepare financial statements and tax returns based on the cash register totals he gave me.
However, if that client had asked the firm to write a letter saying we knew of no improprieties, I doubt he would have gotten one. If we had audited him, and then written a letter saying there were no improprieties, the firm would have been at risk of serious repercussions. So, SOLI's firm, if there were no improprieties prior to 2019, which wasn't audited, could possibly get away with writing that letter, but why would they risk it?
The letter prior to that is telling because the firm probably would not have offered to share information or assist the new firm if there were any serious improprieties they would have to disclose to them. They would be more likely to remain silent.
Lastly, as far as the current accounting firms, reputable accounting firms would walk away from taking on a client who was doing anything illegal, unless it was unintentional and it was something they could correct.
I would conclude SOLI was not doing anything shady when the the last firm left. The accounting firm said they didn't have the resources to handle SOLI's accounting and audit and that was most likely true. The matter of the $10k due to the accounting firm was probably also a factor.