The use of /cancelaura may have inconsistent results. It usually works, but sometimes it lands you in an inconsistent state.
This can be seen when using another common macro (from wowhead guide I think). This is not the solution for your issue, but just showing more uses of that style.
#showtooltip Tiger's Fury
/cancelaura Clearcasting
/cancelaura Predatory Swiftness
/cast Moonfire
/cast Tiger's Fury
Note: The above is an example of a great macro, that sometimes gets you stuck in limbo (still quite useful in Torghast).
Back to your existing macro; The question is why “cancel” the the travel form (unless this is being used to break roots without a GCD)? The risk there is you can get stuck in caster form (noform) and get trained.
Finally, in your macro if you do go into cat form, a GCD is incurred (expected) and the macro stops there (it will not cast the final line of entering stealth). If your objective was to go into stealth quickly, this is slowing you down. If you spam the macro, eventually you will be in cat form, but then you are wasting time casting a /cancelaura (and possibly causing issues induced by “cancelaura” along the way).
If you had to keep using your macro… at a glance, I would modify it as follows:
#showtooltip Prowl
/cancelaura Travel Form
/cast [combat,nostance] Cat Form; /cast !Prowl
To get exactly what you want, you may eventually have several macros that are similar but are used slightly differently. The following are a couple of my macros that may be useful.
Root Shift
If in cat, go bear; If in bear, go cat; If not in form, go cat.
#showtooltip
/cast [form:2] Bear Form(Shapeshift); [form:0/1/3/4/5/6] Cat Form(Shapeshift)
Shadowmeld (NE only)
#showtooltip [mod:shift] Prowl; Shadowmeld
/stopAttack
/cast [combat, mod:shift] Shadowmeld; !Prowl