Yes, and it is fairly common. When someone arrives at a facility on a parole violation hold, they are often placed in administrative segregation or a restricted housing unit during the initial intake period while their status is sorted out. This is not necessarily a punishment. It is a classification and assessment step the facility goes through when someone comes in on a hold rather than as a fresh commitment.
The lockdown period gives the facility time to review the violation, assess the individual, and determine appropriate housing within the general population once the hold is resolved. How long that takes depends on how quickly the parole board or supervising officer processes the violation, when the next hearing is scheduled, and what the facility's current intake workload looks like.
Mail can still reach someone during this period even if phone and visitation access is restricted. Sending a letter right away is a good way to stay connected while the intake process runs its course.