If the computer says you’re in the US illegally, but you have documents that say you are a US citizen, then you are put in custody until the discrepancy can be resolved.
It really depends on whether or not there is a standing deportation order for that person. If not, then it’s a lengthy process where you appear in front of a judge who may release you (yes, low risk aliens are still being released) or held in custody until the trial is held.
If you have a standing deportation order, and your identity is confirmed, then yes, you may be deported quite quickly.
No due process is being denied. If you have a standing deportation order, you can be deported.