Hoping for a solution. Just ran into this and what a snowball. ehCache3 and HttpClient Cache 5.1.1 are compatible. Not so for a any permutation of previous and current versions.
Now upgrading to Spring-Boot 2.5.6 i find that HttpComponentsClientHttpRequestFactory is not compatible with the latest setup of ehCache and HttpClient. RestTemplate cannot be initiated with the ehCache configured HttpClient. There goes the Client-Cache solution.
The search continues.....
Any input much appreciated!