How to do nested and non-nested panel model comparisons?

Question

I am trying multiple panel models based on the identical dataset, which is large with 265,904 observations.

Let's say I am comparing Table 4's models (1), (2), and (3).

Table_4_1 <- plm(DV ~ X1   +    X3 + X4 + X5 + X6, index="firm_id", model="within", data=Survivors_upto_2019) 
Table_4_2 <- plm(DV ~      X2 + X3 + X4 + X5 + X6, index="firm_id", model="within", data=Survivors_upto_2019)  
Table_4_3 <- plm(DV ~      X2 + X3 + X4 + X5 + X6 + X7 + X8 + X9, index="firm_id", model="within", data=Survivors_upto_2019)

summary(Table_4_1)  
summary(Table_4_2)  
summary(Table_4_3)

Table_4_1 and Table_4_2 are unnested, but Table_4_2 and Table_4_3 are nested. Therefore, I used the following commands,

jtest(Table_4_1,Table_4_2)  
pFtest(Table_4_2, Table_4_3)  

For J-test, I obtained the following results.

Estimate Std. Error t value  Pr(>|t|)    
M1 + fitted(M2)  0.95029  0.0034222 277.683 < 2.2e-16 ***  
M2 + fitted(M1)  0.35485  0.0075335  47.103 < 2.2e-16 ***

For pFtest, I got an error.

Warning message:  
In pf(stat, df1, df2, lower.tail = FALSE) : NaNs produced

My questions are:

1. How do I interpret the results from J-statistic?
2. For a panel nested comparison, how should I fix pFtest?