A friend told me he had a weird problem with his western Skyrim surveys and I tried to recreate the situation (which isn't hard).
Long story short: If you collect a survey in western Skyrim you lose two from your inventory instead of one. And if we aren't total idiots you might even lose a survey from your bank thanks to this bug.
Some of you might not have encountred the bug because you collect the surveys when you get them. I collect them until the free eso plus week comes along so I can put the ressources in the crafting back.
My friend went to western skyrim with single copies of surveys but also with stacked suveys. When he collected one of his alchemy surveys he haven't found them again when he returned and he realized that both surveys went missing. After that he went to the woodworking survey and tried to confirm if he actually loses two instead of one survey. After he confirmed that there was a bug he tried to put one of his remaining woodworking surveys in the bank with Ezabi and keep one in the invenotry. After collecting the woodworking survey he tried to speak to Ezabi and get the remaining woodworking survey from the Bank but it was missing.
After that I started recording me when collecting surveys. For now I only encountered the bug where you lose two surveys when collecting one in western Skyrim. And now I have a recording that shows how two surveys were missing from my inventory after I collected a clothing survey in western Skyrim. There could be certain areas where this bug occurs. Currently the only confirmed area is western skyrim. The Bug appeared on PC EU by two persons (me and my friend) and on X-Box (a reddit user told me).
Glenumbra and Craglore appear to be save to collect multiple surveys for now. Would be good if we can track if there are more areas than western Skyrim that are bugged in regards of Survey Maps.
I hope this helps to get rid of the bug. Take care everyone and watch your surveys. You won't get compensated for your surveys by the support. I asked and they said they can't restore lost surveys and didn't offered anything else. So if you try to help figuring out which areas are buged you'll lose value. If you want to play it save keep your surveys on ununsed characters and collect each survey only in stacks of 1.
If you try to keep them in the bank and take one out to collect them watch your bank because you might lose suveys from the bank. I didn't tried to recreat that case because I don't have a Banker like Ezabi. It might be that your Surveys are save in the bank as long as you don't have Ezabi with you. But that is a speculation.