Language regression in 2 year old

[UsefulZombie]

Hoping for some wisdom/advice/reassurance.
DS is 2 years and 4 months old and currently awaiting assessment for autism. I feel quite sure he has ASD. We're very new to this and are trying to learn as much as we can to support and advocate for him as needed.
His language has generally been very good - he's confident with numbers, letters, shapes etc, can name dinosaurs, and recite pages of his favourite books etc. He will also ask for things clearly like specific things for his breakfast or to do certain activities. However, I'm starting to notice words he used to be confident with are used much less frequently, if at all (even with extensive prompting). A few words he used to pronounce clearly are now less clear or mispronounced.
Does anyone have experience of this? Should I be worried?
(Obviously I'm worried regardless, I'm a parent!)
Thank you for reading

My ds had a speech regression about that age. He was joining together words into basic sentences and then he lost all speech. He started regaining it at about 4 and now at 8 I would say he is mainly verbal although not in line with his peers. I've found with ds he develops in his own time and when he's ready.

He used to also lose other skills when he was younger, like he would learn how to roll but then forget it when he learned how to clap etc. It doesn't seem to happen to him so much now, although when he stressed/overwhelmed the speech is always the first thing to go.

It's worth bringing it up with the Health visitor Or GP as they might be able to refer you on to speech and language depending on what is available in your area.