This sounds very much like the frequent problems with microSD cards set up as internal storage (the wording might be “extended internal storage” or similar). Your card is setup like this if the words “portable storage” are missing from Settings > Storage. Under Android 10, the “internal” setup of SD cards causes all sorts of saving and storage issues. You are strongly advised to re-format the card as “portable storage”, see ✏ A little guide to... using SD cards
Furthermore, just 1GB left is definitely way too full. I would always keep 10-20% of your internal storage free.