Assuming "IBM BPM 5.6" means Teamworks / Lombardi 6.x - 7.x or IBM BPM 7.5/8.0 (there is no 5.6), the jump to BAW 19.0.3 is large and these are the things that hurt in practice:
- Heritage coaches and heritage human services: still run, but are deprecated; nothing new can be built with them, Process Designer shows warnings, and the responsive portal (Workplace) does not launch heritage coaches nicely. Plan the conversion to client-side human services + UI Toolkit coach views app by app.
- Removed features: Teamworks 6/7 "Blueprint" artifacts, old Java coaches, Widgets for Business Space, WebSphere Lombardi Edition-style REST calls (/rest/bpm/wle/v1 is still there, the older /portal/jsp endpoints are not), the desktop-only Process Designer flows (web designer is the default).
- JavaScript differences: the server-side engine moved to a newer Rhino - ECMAScript 5 semantics, stricter handling of undefined vs null, XMLDocument handling (E4X removed in BAW 20), date parsing. Scripts that relied on tw.local.x == null vs undefined need testing.
- Toolkit upgrades: every app must be re-pointed to the new System Data / UI Toolkit snapshots; old "Coaches" toolkit views depend on Dojo versions that changed - custom Dojo coach views often break (deprecated dijit widgets).
- Portal customisations: the classic Process Portal is a process app in 8.5.x and BAW 19 - customised copies from 7.x/8.0 must be rebuilt.
- Security: SSO/SPNEGO setup, TLS 1.2 only, CSRF token required on REST (BPMCSRFToken) - external clients that call REST need changes.
- Database and infrastructure: schema upgrades through several releases (7.5 → 8.0 → 8.5 → 8.5.7 → BAW) take time on big instance tables; WebSphere 8.5.5.x fix pack requirements; Java 8.
- Instance migration: in-flight instances migrate to new snapshots only if the flow still has the tokens' activities - test with copies of production data.
Approach that works: side-by-side environment (question 3135), convert one pilot app end to end, measure the coach conversion effort, then plan the rest; keep heritage where it is not touched by users (batch / system processes) and convert user-facing services first.
References
- BAW documentation - migrating from earlier versions
- BAW - deprecated and removed features