After redistribution, R3 learns about network 10.1.1.0/24 via two paths:
+ Internal BGP (IBGP): advertised from R4 with AD of 200 (and metric of 0)
+ OSPF: advertised from R1 with AD of 110 (O E2) (and metric of 20)
Therefore R3 will choose the path with the lower AD via OSPF
But this is a looped path which is received from R3 -> R2 -> R1 -> R3. So when the advertised route from R4 is expired, the looped path is also expired soon and R3 will reinstall the main path from R4.
This is the cause of intermittent connectivity.
We can solve this problem by denying the 10.1.1.0/24 prefix from being redistributed into OSPF on R1. So R3 will not learn this prefix from R1.
Or another solution is to place an OSPF distribute-list inbound on R3 to block the 10.1.1.0/24 prefix from being advertised back to R3.