I've tested this quite a bit, and unfortunately, there's nothing I can do from the app side, this behavior comes from Komga itself. Komic just reports your reading progress to the server, but Komga is the one that validates and saves it. The "invalid progression" error and the fact that EPUBs never quite reach 100% are both handled internally by Komga. Even if Komic sends a full 100% value, Komga will reject it if it doesn't match its own internal logic. So in short, this is a Komga-side issue, not something that can be fixed directly in Komic.
You're right. With EPUBs the progress never reaches 100%. I can reproduce the same behavior in Komga's web UI, so it's not just Komic. I'll work on a more reliable way to detect when a book is actually finished, but it's tricky because EPUB layouts vary and we only have percentages and locators to rely on. About the "Invalid progression" error: the value looks correct in the logs, so I'll dig deeper to find the root cause.
Thanks for aiming for the extra mile above Komga’s features! You have a great app, very clean and well designed ! For « reaching the end » detection, of it’s too complex, don’t bother. It is a nice to have at best. I was thinking it to be easy: no next page anymore or nothing more to scroll…