It is common for the Snort Subscriber Rules to generate errors in Suricata. Search this forum here for other posts about this. Suricata is not Snort. It does not process nor understand all of the Snort rule directives and keywords. For those it does not understand or support, it spits out an error like you see and discards that rule (so that rule is not loaded). Not all the Snort rules will fail, but several hundred will fail (I forget the actual number). Exactly how many fail for you depends on which particular categories and rules you enable (or that get enabled by choosing a Snort IPS Policy).
Emerging Threats has an optimized Suricata ruleset. The Suricata package loads those optimized ET rules when you enable ET rules. Unfortunately, the free ET rules are more limited. The paid ET rules (ET-Pro) which are up-to-date are way more expensive than the Snort rules. Last I checked the ET-Pro rules were $832 per year per device. Compare that to the Snort Subscriber Rules which cost $30 per year for an individual (non-business subscription). There is no corresponding individual subscription for ET-Pro.
Your flowbit errors are likely due to the failure of other dependent rules to load. You can't do anything about this when you run Snort rules with Suricata. This is one of the limitations of Suricata in my view for small non-business users. The only affordable rules packages are not complete in their coverage. Even when you use Snort Rules, several of them won't load in Suricata.
You may be better served to switch to Snort and use the paid Snort Subscriber Rules; unless you have the coin to pay Proofpoint $832 a year for an Emerging Threats Pro subscription.