The Spectre bug which is concerned with side channel problems has been a long standing problem. The branch prediction design which was done to speed up execution has been at issue.
Speculative execution is an optimization technique that modern processors implement to increase performance. The performance increase is achieved through the processor executing some operations before it knows they are needed by the program. This speculative work saves time compared to waiting until an operation is required from the CPU.
The branch prediction is not isolated so its possible for another thread to attack it. To fix the problem will require a very complex redesign of the core ALU.
We have disliked hyperthreading as we prefer full cores as OpenMP etc is designed that way. All of the problems have been due largely to the multicore architecture. The old 8088 never had to deal with modem problems.
The Intel Ice Lake has been modified to fix some problems but most are at the OS level. Ice Lake is still being made in the 14nm line while work in more fixes in the works. Perhaps Tiger Lake down the road will resolve more problems at the hardware level.
Intel continues to have problems with yields at 10nm and until they can figure that out 14nm is here to stay.
Meanwhile AMD has to be cautious with design as well. The next series of processors is expected soon.