A működési hiba és a meghibásodás komolyak.

Hungarian often leaves out the verb to be in the present tense, third person.

So instead of saying something like A működési hiba és a meghibásodás komolyak vannak, Hungarian simply says:

A működési hiba és a meghibásodás komolyak.

This is completely normal.
Compare:

• A hiba komoly. = The error is serious.
• A hibák komolyak. = The errors are serious.

In past or future tense, however, a form of van / volt / lesz would appear.

Because the subject is made up of two things joined by és (and):

• a működési hiba
• a meghibásodás

Together, they form a plural subject, so the predicate adjective must also be plural:

• komoly = serious
• komolyak = serious (plural)

This is similar to English The error and the failure are serious, not is serious.

Here, -ak is the plural ending on the adjective.

• komoly = serious
• komolyak = serious ones / serious (when referring to plural subjects)

In Hungarian, when an adjective is used as the predicate in a sentence like this, it agrees in number with the subject.

So:

• A meghibásodás komoly. = The breakdown is serious.
• A működési hiba és a meghibásodás komolyak. = The operating error and the breakdown are serious.

Hungarian normally repeats the definite article before each noun in a coordinated phrase if both nouns are definite.

So:

• a működési hiba és a meghibásodás = the operating error and the breakdown

This is very natural in Hungarian.
English can also repeat the, but often does not need to emphasize it as much.

If both nouns are definite, repeating a/az is the standard, expected pattern.

They are related, but not identical.

• működési hiba literally means something like operational error, malfunction, or functioning error
• meghibásodás means breakdown, failure, or a becoming faulty

A helpful way to think about it:

• hiba = an error, fault, defect
• meghibásodás = the event/state of something going wrong or breaking down

Also:

• működési comes from működés = operation, functioning
• so működési hiba is literally an error of operation/functioning

Depending on context, the two may overlap in translation, but Hungarian keeps them as distinct nouns here.

működési is an adjective formed from the noun működés (operation, functioning).

• működés = operation/functioning
• működési = operational / relating to operation

So:

• működési hiba = operational error / functioning error

In Hungarian, descriptive adjectives normally come before the noun, just as in English:

• komoly probléma = serious problem
• működési hiba = operational error

The -i ending is very common when making an adjective meaning related to X.

It is a noun.

It comes from the verb meghibásodik, which means to break down, to fail, or to become faulty.

So:

• meghibásodik = it breaks down
• meghibásodás = breakdown / failure

This noun ending -ás / -és is very common in Hungarian for forming action or process nouns from verbs.

For example:

• indít = start
• indítás = starting

So meghibásodás is literally something like the process/event of becoming faulty.

That is the normal position in a simple Hungarian equational sentence like this.

Structure:

• A működési hiba és a meghibásodás = the subject
• komolyak = the predicate adjective

So the sentence is essentially:

The operational error and the breakdown are serious.

Hungarian often places the descriptive part after the subject in this kind of sentence.

You could change word order for emphasis in some contexts, but this neutral version is very natural.

In standard Hungarian, yes, that would be wrong here.

Because the subject is plural in meaning (X and Y), the predicate adjective should be plural too:

• correct: A működési hiba és a meghibásodás komolyak.
• incorrect here: A működési hiba és a meghibásodás komoly.

Hungarian is stricter than English in some cases about showing plural agreement in this kind of sentence.

A rough pronunciation guide:

• működési ≈ mew-kuh-day-shee
• meghibásodás ≈ meg-hee-baa-sho-daash

A few useful notes:

• ű is a long front rounded vowel, with no exact English equivalent
• ö is also a rounded front vowel, somewhat like German ö
• s in Hungarian is pronounced sh
• sz is pronounced s
• cs is pronounced ch
• stress is almost always on the first syllable:
  • MŰködési
  • MEGhibásodás

In isolation, komolyak is simply the plural form of serious, and in this sentence it functions as the predicate adjective: are serious.

So in this sentence, the natural interpretation is definitely:

The operating error and the breakdown are serious.

Hungarian adjectives can sometimes behave a bit like nouns in other contexts, but here the structure clearly signals a normal predicate adjective, not serious ones as a separate noun phrase.