I want to echo the sentiment that 802.11r is not needed in most situations. It is a common misconception that this standard is either required for roaming or that it will dramatically increase roaming performance (reduce roaming latency, etc.).
Fast roaming (802.11r) is not required for roaming to work in general. Roaming is a client (sta mode) side operation and relies on two factors:
- A well tuned RF environment -- that is, the placement, channel selection and power level adjustment (i.e. reduced power) such that neighboring APs have a small region of overlap. I really like the way this video explains the process of tuning your APs (it discusses it in the context of Unifi, but it applies to all wifi).
- Well developed logic in the client (STA) devices to make intelligent roaming choices.
When these two things are done well, roaming can be nearly seamless at human scale, and nothing more is required in general.
802.11r adds some additional coordination between the APs and the STA devices as they move through a space to help improve the speed at which the STA can disconnect from one AP, connect to the next, and reestablish network connectivity. This only adds value if the APs have been properly tuned... if they're not well tuned, the performance may actually decrease with 802.11r. Beyond that, some devices don't work well with 802.11r enabled... in this situation, 802.11r can also decrease performance to the point of devices not being able to join or maintain a connection on the network.
Have you started with point 1 above?