To the OP:
Valid (as opposed to neurotic) shame can legitimately persist after a valid confession. Lingering shame serves a spiritual purpose, in reminding us of how we have hurt ourselves, specific others, The Church community, and Our Lord. Therefore, it increases humility, which is extremely beneficial for us in growing in the spiritual life. It makes us conscious of our need for mercy and therefore tends to prevent us from becoming complacent that we won’t need mercy again. Finally, that consciousness may make us interested in repairing a past sin or several past sins, by doing opposing works of virtue.
Thus, to benefit spiritually from the shame, we can practice honesty when another opportunity presents itself – such as admtting on a form or in person that we are not eligible for such-and-such benefit, reduced cost, etc., especially when in such applications or petitions “no one would know” otherwise. (We are choosing not to cheat.) At those opportunities we can make an interior, conscious act of reparation to God for past compromises to honesty.
There is no sin in my life, for which I have been forgiven, that I am not still ashamed about. And that goes back to childhood. I would think that if my shame had vanished, perhaps I was not previously contrite enough over that sin. But the Devil can tempt us to use that shame to avoid God (and our next confession), rather than to approach him with acknowledgement of shame. (Because shame is painful! It wounds are cherished pride and false sense of ‘worth,’ superiority, and self-sufficiency.) We only need to make certain that we are not allowing shame to overwhelm our hope and trust. Avoiding God due to lack of trust (despair, whether prompted by shame or anything else) is the danger.
So I try not to let shame become a barrier to prayer, the sacraments, and the theological virtues. If/when we feel overwhelmed by shame, it’s important to acknowledge that directly and honestly before God, and to lay our shame at the feet of our merciful Father and our merciful Redeemer. People way too often forget that God works in and through our feelings. Shame is a feeling. It should be offered to Our Lord at Lent in union with the Passion.