I updated my main BBS to A47C from 2/12 and it looks to me files are causing the busy issues I'm seeing:
----------------- MUTIL v1.12 A47 2021/02/12 Sun, Feb 21 2021 (loglevel 3)
+ Feb 21 19:04:29 Startup using mailin.ini
- Feb 21 19:04:29 EXEC ImportEchoMail
- Feb 21 19:04:29 EXEC LinkMessages
- Feb 21 19:04:29 EXEC FileToss
+ Feb 21 19:04:29 Process: Toss FDN/TIC Files
+ Feb 21 19:04:29 Waiting for BUSY nodes

So it looks to me like junk in /mystic/files/badfiles and I should likely just delete everything in the badfiles, does that sound right to you?
Most of it seems to be from years past and I deleted it once before, but that was before I upgraded to the 2/12 alpha, but it's re-appeared. Not sure why,

--- Mystic BBS v1.12 A47 2021/02/12 (Raspberry Pi/32)
* Origin: Mystic Pi BBS bcw142.zapto.org (21:1/145)