The game autosaved while I was sieging. When I reloaded the autosave I got a attack or leave message (the two options). No option to lead an assault like you do when you siege. Had to choose leave and then start the siege again. This has happened in at least three different sieges at different castles. I'll upload a save file next time it happens.
Game Version: 1.4.1.233641
No mods
OS: Microsoft Windows 10 Pro
Version 10.0.18363 Build 18363
ASUS x64-based PC
GPU: 2 in SLI - Nvidia Geforce GTX 970
CPU: Intel(R) Core(TM) i7-5930K CPU @ 3.50GHz, 3501 Mhz, 6 core, 12 logical processor
BIOS American Megatrends Inc. 1701, 14.08.2015
SMBIOS-version 2.8
BIOS-mode UEFI
RAM: HyperX Fury 2133MHz 64GB (8x8GB)
Motherboard: ASUSTeK COMPUTER INC. - RAMPAGE V EXTREME
Samsung SSD 840 EVO 1TB