The problem that arises from using qui or que is that the subject of your clause changes and so do the direct object. Since your clauses are conjugated with past participles using the avoir auxiliary, the direct object is a key component in understanding how to make them agree because the past participle will agree with the direct object if, and only if, it is placed before the verb.

If we take the clause from your first example:

[L]es récents événements malheureux qui l’ont { frappée / frappés }.

The direct object here is “l’“, which refers to “XXX industries”, and it is place right before the verb. Therefore, since it seems that this entity is feminine singular in this sentence, so the past participle should agree that way.

Ses préoccupations quant à la capacité de XXX industries de se remettre des récents événements malheureux qui l’ont frappée sont tout à fait infondées.

You can read more about the general rule of past participle conjugation with avoir with a relative pronoun (French post).

As Kareen mentioned, when using the auxiliary avoir, the past participle agrees with a preceding direct object.

Ses préoccupations quant à la capacité de XXX industries de se
remettre des récents événements malheureux qui l’ont { frappée /
frappés } sont tout à fait infondées.

In the preceding sentence, it seems like the direct object in your sentence is “la,” which refers back to “XXX industries.” In other words, you’re talking about

“les récents événements malheureux qui ont frappé XXX industries.”

You aren’t saying that the événements have frappés themselves (and anyway, in that case you’d use a reflexive pronoun and the auxiliary être). In your sentence, événements corresponds to the subject pronoun qui: it is not the object, so it does not affect the past participle.

If “XXX industries” is a singular feminine noun (I don’t understand how this works—I would guess it should be plural—but I don’t know anything about this area of French grammar) you should use “frappée.”

You know the rule with COD agreement, so let’s make it simple:

[…] des récents événements malheureux qui l’ont frappée […]

… because:

les événements (sujet) ont frappé XXX Industries (COD).

But:

[…] des récents événements malheureux qu’elle a vécus […]

… because:

elle (sujet) a vécu les événements (COD).