So, we can agree that abuses in the Church can result in invalid sacraments.
Some abuses - yes. Others - no
Someone has yet to answer if this issue was encountered in the ancient, or not so ancient, church, and how it was regarded.
Without researching it, I know both Cyprian and Augustine considered the issue. How much further back do you want to go? Look 'em up.
We can construct a hierarchy of severity in case of an invalid sacraments.
No you can’t because invalid is invalid. You could construct a hierarchy of severity surrounding the facts of why the sacrament was invalid and how that creates problems. But, any invalid sacrament simply is not a sacrament.
I think the most important case consists of the sacraments that are not to be repeated: baptism, confirmation and ordination.
Maybe…need more info for such a broad statement.
An invalid baptism is an especially severe problem, since it leads to the invalidity of all other sacraments.
The sacraments are valid ex opere operato. Their validity is not dependent on the state of grace of the recipient (or the minister for that matter). Whether the grace of the sacrament flows to the recipient is a different matter. Thus, an invalidly baptized person may receive a validly confected Eucharist - but the grace for that reception is not conveyed to that person…yet, the Eucharist is valid. True, as you say above, that would be a serious matter, but the validity of the sacrament depends only on the proper matter, proper form and proper intent of the minister of the sacrament.
I suppose where the valid matter is a baptized person - marriage, ordination -that a special case, but again it’s not invalidity per se as a radical sanation can correct the defect in the marriage. If the sacrament is invalid - it simply doesn’t exist. Not sure if an ex post baptism could remedy the defect in ordination. Without research, my guess is yes it would.
Occasional invalid Eucharist is probably not critical for salvation, an unnoticed invalid absolution is not a problem, if it is not going to be the last one, since the next valid absolution will compensate for it.
who knows…maybe it’s quite severe…what of viaticum?
The issue of invalid acts and the uncertainty they bring is not unique to the sacraments. It is also dealt with in civil law. Legal acts and contracts can be invalid for a multitude of reasons. There the solution is bona fides rules and statutes of limitations. Bona fides rules that that if a legal act is publicly recognized and there is no apparent reason to doubt its validity, the beneficient gets to enjoy its effects even though it were objectively invalid. Statutes of limitations maintain that the validity of an act must be challenged within a reasonable time, and it will not be investigated later on. Together, these principles provide legal certainty. As far as I know, the Catholic Church has not authoritatively adopted any of these principles with regard to invalid baptisms or other sacraments.
You, as many here, seem to confuse “invalidity” with “illiceity.”
An invalid sacrament is not a sacrament at all. It can’t be made a sacrament as one never existed. The civil legal issue you raise is more properly associated with liceity. Liceity refers to the legality of the manner in which the sacrament is performed. As such, there are many illicit acts surrounding the sacraments - some result in illegal but valid sacraments and some result in no sacrament at all (invalidity). Liceity concerns the laws for the performance of the sacraments to assure validity.
Sometimes people raise Ecclesia Supplet as an answer - but that deals only with incomplete sacraments - a liceity issue and/or a reception issue - but it can’t make valid what is invalid. Ecclesia supplet doesn’t work with invalidity because it’s not that the sacrament is incomplete in some way - it’s non-existent.
Many discussions here concern illicit actions of the priest and those illicit actions lead people to wonder if the sacrament is valid -All of which is proof of the need to confect the sacraments in accordance with the laws - so that through a licit ritual validity is not questioned.
Now in extreme situations there may be reasons to not follow the law, e.g., priests in concentration camps who used a grape (hopefully fermented to a bit of wine that almost certainly wasn’t at the legal alcoholic minimum content of the law at that time) yet, through God’s goodness probably was valid though illicit. Here is an example where a clearly illicit and possibly invalid sacrament was confected with little culpability if any on the part of the priest.