The main things that are slow are loading the app and opening the app, loading the messages, and receiving the messages. On my phone, this is much slower than Telegram, and on my computer, the WhatsApp program doesn't even work have the time -- it just gets stuck in the loading process.
Signal is not as bad, but can still take a minute or two to update everything on my computer. The phone app is better.
Sounds more like your personal problem.
I live in Germany and use both. None do that and as I'm "the IT guy" for many people at work an din private, I'd have heard about it. Hell, the whole continent would have heard about it as whatsapp is widely used.
My Signal also doesn't do that.
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