Same problem here, but I found some sort of workaround.
I have a Windows laptop, and Android phone and an iPad in sync.
To make the ignore list work on the phone I had to do many attempts. The solution was to copy the custom IgnoreList file from the laptop over the phone, as otherwise it wouldn't sync at all, not even doing a rescan of the folder. An this has to be done every time I make a change to the ignoreList. Quite impractical and annoying.
On the iPad instead, there is no hidden Sync folder thus there is no way to copy the ignoreLIst file. All the files and folders are just there, but the unwanted ones are greyed out instead of being totally filtered out, unable to be downloaded and with a spin icon, as if the app is trying do sync them, which seems a bug to me.
I don't know if the iOS app is intended to work like so, but honestly is quite confusing and not practical. I have to scroll and browse through a lot of unwanted folders and files for no reason.
I switched from Syncthing Fork to Resilio because of the its limitations on iOS and of writing on the SD card under Android, but so far the experience with Resilio is quite frustrating and confusing, even though it's easier to set up. What a pity.
Would be nice to have a feedback and a solution about these issues!