@gopala007 , Namaste ji
(a) Generally with the first entry as F-1, one is allowed a five calendar year reprieve from having to count days present ( "exempt" status ) towards Substantial Presence Test. So if you changed your F-1 status and then came back to F-1, you still have ONLY the original five calendar years and/or the unused portion thereof.
(b) Thus I would , absent any other contravening facts/ circumstances, that if you entered the country in 2020, your max availability of exempt status is till m12/31/2024. So if you became ineligible for exempt status for the period 10/01/2022 through 11/01/2023, then you have only 01/01/2024 through 12/31/2024 as the remainder exempt period. Note that this depends on the exact circumstances and facts in your case.
(c) The FICA tax has really nothing to do with "exempt " status. It depends on your work status ( training , school education status) -- whether you are a trainee or an actual employee. So if you are allowed to work /earn on the school premises or as a trainee / part of your education/ research etc. you are temporarily present and therefore immune from FICA requirements.
Please tell me more about --- when did you arrive in the USA, was this your first entry for any reason, which country are you from, why did you change to H1-B ( not OPT? ), are you married and if so to whom -- US person or an NRA, etc. etc.
I will circle back once I hear from you
pk
