When you leave a 401(k) at a past employer, you are susceptible to changes with that former employer and their plan, including administrative or other fees that they would normally cover for active participants or current employees. Be careful and consult a trusted financial advisor.
https://www.forbes.com/sites/cicelyjones/2025/03/24/why-you-shouldnt-leave-your-401k-with-a-past-employer/