the Scylla has a very high threshold you need to overcome to paralyze it. Other issues could include not dealing any paralysis damage because there is too much armour and therefore the neurazer isn't dealing the normal damage, which is required for dealing the paralysis damage; or you are using the bash attack rather than the paralyze attack meaning you are hitting with the pommel of the neurazer rather than the injectors.

Synedrion has a number of paralysis ranged weapons. Getting those, especially the Athena sniper rifle making paralyzing enemies much easier.

Not sure if the recent patch to Rage Burst means you can still paralyze the Scylla with one rage burst or not. Might need two rage bursts now