Problems with loading from asset bundles after Unity upgrade

We are using Unity 2017.1.1 and trying to upgrade to Unity 2017.4.12 (LTS).

Our game loads different asset bundles at runtime. These were built using 2017.1.1. At runtime i am seeing these errors:

Failed to load GpuProgram from binary shader data in 'Particles/Alpha Blended'
Failed to load GpuProgram from binary shader data in 'Unlit/Transparent'.

and a few others (for other shaders).

This affects our game as particles and other images appear with visual artifacts or other graphical issues.
I read the upgrade guides and there were no apparent issues that should cause us any breaking changes.

Is this a known issue with 2017.4.12? what can we do to resolve it ?

UPDATE: i just tested this again by rebuilding the asset bundle using 2017.4.12 and it worked. i would really like to avoid rebuilding all of our content using the newer Unity. is there any way to avoid it ?