You are misreading the Canons.
Here they are again.
Canon 1247
On Sundays and other holy days of obligation the faithful are bound to participate in the Mass; they are also to abstain from those labors and business concerns which impede the worship to be rendered to God, the joy which is proper to the Lord’s Day, or the proper relaxation of mind and body.
Canon 1248
- The precept of participating in the Mass is satisfied by assistance at a Mass which is celebrated anywhere in a Catholic rite either on the holy day or on the evening of the preceding day.
- If because of lack of a sacred minister or for other grave cause participation in the celebration of the Eucharist is impossible, it is specially recommended that the faithful take part in the liturgy of the word if it is celebrated in the parish church or in another sacred place according to the prescriptions of the diocesan bishop, or engage in prayer for an appropriate amount of time personally or in a family or, as occasion offers, in groups of families.
Section 2 of Canon 1248 is not addressing the attending of a Mass the evening of the preceding day, section 1 addresses that and does not say that a grave cause is necessary.
Section 2 is addressing a communion service with the Liturgy of the Word because the lack of a sacred minister. This would require a grave cause.
This is plan to see as the first sentence of section 2 says “participation in the celebration of the Eucharist is impossible.” It does not speak to attending Mass on the evening before, which, again, is addressed in section 1 and in canon 1247, both of which say its is acceptable and does not state that a “grave cause” is necessary.
On a side note, I find it odd that lay people push this idea especially when a priest (or a
seminarian) who is trained by the Church speaks on the matter.