Learn Hardcore Russian: Из-за слабого сигнала приложение работало медленно. - Because of a weak signal, the app worked slowly.

Because the compound preposition из‑за always takes the genitive case. Сигнал is a masculine noun, so its genitive singular is сигнала, and the adjective must agree in case, number, and gender: слабого сигнала. More examples:

из‑за дождя (because of the rain)
из‑за пробки (because of a traffic jam)

How is из‑за spelled and what exactly does it mean?

Spelling: always with a hyphen and a space after it: из‑за
- [GENITIVE].
Meanings: 1) Causal: из‑за слабого сигнала = because of a weak signal (common in this sentence). 2) Spatial: из‑за угла = from behind the corner. Never write it as из за (no hyphen) or replace it with из here; из alone doesn’t express cause.

Can the cause phrase move? Is Приложение работало медленно из‑за слабого сигнала also correct?

Yes. Russian word order is flexible. Both are natural:

Из‑за слабого сигнала приложение работало медленно. (fronted cause for emphasis)
Приложение работало медленно из‑за слабого сигнала. (neutral flow; places new info at the end) Choose position for emphasis and flow; no comma is needed in either version.

Why is it работало and not работал or работала?

Past‑tense verbs agree with the subject’s gender and number. Приложение is neuter singular, so past tense is neuter: работало. Patterns:

masc: он работал
fem: она работала
neuter: оно работало
plural: они работали

Why use the adverb медленно instead of the adjective медленное?

Because we’re modifying the verb (how it worked), not describing a noun. In Russian, actions are modified by adverbs:

работало медленно = it worked slowly. If you say приложение медленное, you’re describing a property of the app (the app is slow), not how it worked in this instance.

What aspect is работало? Could I use a perfective form?

Работало is imperfective past; it describes an ongoing or repeated process. A perfective like заработало means “started working,” which changes the meaning. To express a change into a slow mode, you could say: Приложение стало работать медленно.

Is there any nuance to из‑за? Does it sound negative?

Often, yes. Из‑за tends to be used for causes with an undesirable or problematic effect. For neutral or formal phrasing, you might use по причине or вследствие. For positive causes, Russian prefers благодаря (+ dative): Благодаря сильному сигналу приложение работало быстро.

How would I say the same idea with a full clause instead of a noun phrase?

Use:

Приложение работало медленно, потому что сигнал был слабый/слабым. Both слабый (short predicate in nominative) and слабым (instrumental after был) are acceptable; the instrumental can feel a bit more formal or stylistic. With из‑за того, что, you’d write: … из‑за того, что сигнал был слабый, and you need a comma before что.

Could I say Приложение было медленным here?

It’s grammatical, but less idiomatic for performance in context. Было медленным attributes a general property (“the app was slow”), whereas работало медленно focuses on how it performed. With a specific cause like из‑за слабого сигнала, Russian typically prefers the adverbial phrase: … работало медленно.

What are natural alternatives to слабого сигнала?

из‑за плохого сигнала (poor signal; broader than “weak”)
из‑за слабой связи (weak connection)
из‑за низкого уровня сигнала (low signal level; more technical)
из‑за плохого соединения (poor connection) All keep genitive after из‑за: слабой связи, плохого соединения, etc.

Are there colloquial ways to say “worked slowly” about an app?

Yes:

Приложение тормозило. (colloquial “was lagging/slow”)
Приложение лагало. (slang from English “lag”)
Приложение подвисало. (kept freezing/hanging intermittently) These are informal; работало медленно is neutral and standard.

Any pronunciation or stress tips for this sentence?

из‑за́ (often pronounced with a doubled
сла́бого (stress on first а)
сигна́ла (stress on а)
приложе́ние (stress on е́)
рабо́тало
ме́дленно (double нн in spelling; no extra length in speech) A simple transliteration: iz‑za slabogo signala prilozhéniye rabótalo médlenno.

Do I need any commas in the original sentence?

No. Из‑за слабого сигнала приложение работало медленно. has no comma. You add a comma only if you introduce a clause, e.g., …, потому что … or … из‑за того, что …

If I change the nouns, how do the forms change?

They must match case, gender, and number:

из‑за слабой связи приложение работало медленно (fem. gen. sg.: слабой связи)
из‑за слабых сигналов приложения работали медленно (plural gen.: слабых сигналов; plural verb работали)

Could I say со слабым сигналом instead of из‑за слабого сигнала?

Not for cause. С(о) + instrumental means “with” (accompaniment or condition), not “because of.” Со слабым сигналом would sound like “with a weak signal” rather than stating a cause. Use из‑за for causation.